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doc/en_US.ISO8859-1/books/handbook/disks/chapter.xml
Ed Maste b1c526c650 UFS snapshots are read-only 
Change the snapshot example to show creating the md(4) read-only, in order
to avoid a warning.
2014-05-09 17:39:32 +00:00

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<?xml version="1.0" encoding="iso-8859-1"?>
<!--
The FreeBSD Documentation Project
$FreeBSD$
-->
<chapter xmlns="http://docbook.org/ns/docbook"
xmlns:xlink="http://www.w3.org/1999/xlink" version="5.0"
xml:id="disks">
<title>Storage</title>
<sect1 xml:id="disks-synopsis">
<title>Synopsis</title>
<para>This chapter covers the use of disks and storage media in
&os;. This includes <acronym>SCSI</acronym> and
<acronym>IDE</acronym> disks, <acronym>CD</acronym> and
<acronym>DVD</acronym> media, memory-backed disks, and
<acronym>USB</acronym> storage devices.</para>
<para>After reading this chapter, you will know:</para>
<itemizedlist>
<listitem>
<para>How to add additional hard disks to a &os;
system.</para>
</listitem>
<listitem>
<para>How to grow the size of a disk's partition on
&os;.</para>
</listitem>
<listitem>
<para>How to configure &os; to use <acronym>USB</acronym>
storage devices.</para>
</listitem>
<listitem>
<para>How to use <acronym>CD</acronym> and
<acronym>DVD</acronym> media on a &os; system.</para>
</listitem>
<listitem>
<para>How to use the backup programs available under
&os;.</para>
</listitem>
<listitem>
<para>How to set up memory disks.</para>
</listitem>
<listitem>
<para>What file system snapshots are and how to use them
efficiently.</para>
</listitem>
<listitem>
<para>How to use quotas to limit disk space usage.</para>
</listitem>
<listitem>
<para>How to encrypt disks and swap to secure them against
attackers.</para>
</listitem>
<listitem>
<para>How to configure a highly available storage
network.</para>
</listitem>
</itemizedlist>
<para>Before reading this chapter, you should:</para>
<itemizedlist>
<listitem>
<para>Know how to <link linkend="kernelconfig">configure and
install a new &os; kernel</link>.</para>
</listitem>
</itemizedlist>
</sect1>
<sect1 xml:id="disks-adding">
<info>
<title>Adding Disks</title>
<authorgroup>
<author>
<personname>
<firstname>David</firstname>
<surname>O'Brien</surname>
</personname>
<contrib>Originally contributed by </contrib>
</author>
</authorgroup>
</info>
<indexterm>
<primary>disks</primary>
<secondary>adding</secondary>
</indexterm>
<para>This section describes how to add a new
<acronym>SATA</acronym> disk to a machine that currently only
has a single drive. First, turn off the computer and install
the drive in the computer following the instructions of the
computer, controller, and drive manufacturers. Reboot the
system and become
<systemitem class="username">root</systemitem>.</para>
<para>Inspect <filename>/var/run/dmesg.boot</filename> to ensure
the new disk was found. In this example, the newly added
<acronym>SATA</acronym> drive will appear as
<filename>ada1</filename>.</para>
<indexterm><primary>partitions</primary></indexterm>
<indexterm>
<primary><command>gpart</command></primary>
</indexterm>
<para>For this example, a single large partition will be created
on the new disk. The <link
xlink:href="http://en.wikipedia.org/wiki/GUID_Partition_Table">
<acronym>GPT</acronym></link> partitioning scheme will be
used in preference to the older and less versatile
<acronym>MBR</acronym> scheme.</para>
<note>
<para>If the disk to be added is not blank, old partition
information can be removed with
<command>gpart delete</command>. See &man.gpart.8; for
details.</para>
</note>
<para>The partition scheme is created, and then a single partition
is added:</para>
<screen>&prompt.root; <userinput>gpart create -s GPT ada1</userinput>
&prompt.root; <userinput>gpart add -t freebsd-ufs ada1</userinput></screen>
<para>Depending on use, several smaller partitions may be desired.
See &man.gpart.8; for options to create partitions smaller than
a whole disk.</para>
<para>A file system is created on the new blank disk:</para>
<screen>&prompt.root; <userinput>newfs -U /dev/ada1p1</userinput></screen>
<para>An empty directory is created as a
<emphasis>mountpoint</emphasis>, a location for mounting the new
disk in the original disk's file system:</para>
<screen>&prompt.root; <userinput>mkdir /newdisk</userinput></screen>
<para>Finally, an entry is added to
<filename>/etc/fstab</filename> so the new disk will be mounted
automatically at startup:</para>
<programlisting>/dev/ada1p1 /newdisk ufs rw 2 2</programlisting>
<para>The new disk can be mounted manually, without restarting the
system:</para>
<screen>&prompt.root; <userinput>mount /newdisk</userinput></screen>
</sect1>
<sect1 xml:id="disks-growing">
<info>
<title>Resizing and Growing Disks</title>
<authorgroup>
<author>
<personname>
<firstname>Allan</firstname>
<surname>Jude</surname>
</personname>
<contrib>Originally contributed by </contrib>
</author>
</authorgroup>
</info>
<indexterm>
<primary>disks</primary>
<secondary>resizing</secondary>
</indexterm>
<para>A disk's capacity can increase without any changes to the
data already present. This happens commonly with virtual
machines, when the virtual disk turns out to be too small and is
enlarged. Sometimes a disk image is written to a
<acronym>USB</acronym> memory stick, but does not use the full
capacity. Here we describe how to resize or
<emphasis>grow</emphasis> disk contents to take advantage of
increased capacity.</para>
<para>Determine the device name of the disk to be resized by
inspecting <filename>/var/run/dmesg.boot</filename>. In this
example, there is only one <acronym>SATA</acronym> disk in the
system, so the drive will appear as
<filename>ada0</filename>.</para>
<indexterm><primary>partitions</primary></indexterm>
<indexterm>
<primary><command>gpart</command></primary>
</indexterm>
<para>List the partitions on the disk to see the current
configuration:</para>
<screen>&prompt.root; <userinput>gpart show <replaceable>ada0</replaceable></userinput>
=> 34 83886013 ada0 GPT (48G) [CORRUPT]
34 128 1 freebsd-boot (64k)
162 79691648 2 freebsd-ufs (38G)
79691810 4194236 3 freebsd-swap (2G)
83886046 1 - free - (512B)</screen>
<note>
<para>If the disk was formatted with the <link
xlink:href="http://en.wikipedia.org/wiki/GUID_Partition_Table">
<acronym>GPT</acronym></link> partitioning scheme, it may show
as <quote>corrupted</quote> because the <acronym>GPT</acronym>
backup partition table is no longer at the end of the
drive. Fix the backup
partition table with
<command>gpart</command>:</para>
<screen>&prompt.root; <userinput>gpart recover <replaceable>ada0</replaceable></userinput>
ada0 recovered</screen>
</note>
<para>Now the additional space on the disk is available for
use by a new partition, or an existing partition can be
expanded:</para>
<screen>&prompt.root; <userinput>gpart show <replaceable>ada0</replaceable></userinput>
=> 34 102399933 ada0 GPT (48G)
34 128 1 freebsd-boot (64k)
162 79691648 2 freebsd-ufs (38G)
79691810 4194236 3 freebsd-swap (2G)
83886046 18513921 - free - (8.8G)</screen>
<para>Partitions can only be resized into contiguous free space.
Here, the last partition on the disk is the swap partition, but
the second partition is the one that needs to be resized. Swap
partitions only contain temporary data, so it can safely be
unmounted, deleted, and then recreated after resizing other
partitions.</para>
<screen>&prompt.root; <userinput>swapoff <replaceable>/dev/ada0p3</replaceable></userinput>
&prompt.root; <userinput>gpart delete -i <replaceable>3</replaceable> <replaceable>ada0</replaceable></userinput>
ada0p3 deleted
&prompt.root; <userinput>gpart show <replaceable>ada0</replaceable></userinput>
=> 34 102399933 ada0 GPT (48G)
34 128 1 freebsd-boot (64k)
162 79691648 2 freebsd-ufs (38G)
79691810 22708157 - free - (10G)</screen>
<warning>
<para>There is risk of data loss when modifying the partition
table of a mounted file system. It is best to perform the
following steps on an unmounted file system while running from
a live <acronym>CD-ROM</acronym> or <acronym>USB</acronym>
device. However, if absolutely necessary, a mounted file
system can be resized after disabling GEOM safety
features:</para>
<screen>&prompt.root; <userinput>sysctl kern.geom.debugflags=16</userinput></screen>
</warning>
<para>Resize the partition, leaving room to recreate a swap
partition of the desired size. This only modifies the size of
the partition. The file system in the partition will be
expanded in a separate step.</para>
<screen>&prompt.root; <userinput>gpart resize -i <replaceable>2</replaceable> -a 4k -s <replaceable>47G</replaceable> <replaceable>ada0</replaceable></userinput>
ada0p2 resized
&prompt.root; <userinput>gpart show <replaceable>ada0</replaceable></userinput>
=> 34 102399933 ada0 GPT (48G)
34 128 1 freebsd-boot (64k)
162 98566144 2 freebsd-ufs (47G)
98566306 3833661 - free - (1.8G)</screen>
<para>Recreate the swap partition:</para>
<screen>&prompt.root; <userinput>gpart add -t freebsd-swap -a 4k <replaceable>ada0</replaceable></userinput>
ada0p3 added
&prompt.root; <userinput>gpart show <replaceable>ada0</replaceable></userinput>
=> 34 102399933 ada0 GPT (48G)
34 128 1 freebsd-boot (64k)
162 98566144 2 freebsd-ufs (47G)
98566306 3833661 3 freebsd-swap (1.8G)
&prompt.root; <userinput>swapon <replaceable>/dev/ada0p3</replaceable></userinput></screen>
<para>Grow the <acronym>UFS</acronym> file system to use the new
capacity of the resized partition:</para>
<note>
<para>Growing a live <acronym>UFS</acronym> file system is only
possible in &os; 10.0-RELEASE and later. For earlier
versions, the file system must not be mounted.</para>
</note>
<screen>&prompt.root; <userinput>growfs <replaceable>/dev/ada0p2</replaceable></userinput>
Device is mounted read-write; resizing will result in temporary write suspension for /.
It's strongly recommended to make a backup before growing the file system.
OK to grow file system on /dev/ada0p2, mounted on /, from 38GB to 47GB? [Yes/No] <userinput>Yes</userinput>
super-block backups (for fsck -b #) at:
80781312, 82063552, 83345792, 84628032, 85910272, 87192512, 88474752,
89756992, 91039232, 92321472, 93603712, 94885952, 96168192, 97450432</screen>
<para>Both the partition and the file system on it have now been
resized to use the newly-available disk space.</para>
</sect1>
<sect1 xml:id="usb-disks">
<info>
<title><acronym>USB</acronym> Storage Devices</title>
<authorgroup>
<author>
<personname>
<firstname>Marc</firstname>
<surname>Fonvieille</surname>
</personname>
<contrib>Contributed by </contrib>
</author>
</authorgroup>
</info>
<indexterm>
<primary>USB</primary>
<secondary>disks</secondary>
</indexterm>
<para>Many external storage solutions, such as hard drives,
<acronym>USB</acronym> thumbdrives, and <acronym>CD</acronym>
and <acronym>DVD</acronym> burners, use the Universal Serial Bus
(<acronym>USB</acronym>). &os; provides support for
<acronym>USB</acronym> 1.x, 2.0, and 3.0 devices.</para>
<note>
<para><acronym>USB</acronym> 3.0 support is not compatible with
some hardware, including Haswell (Lynx point) chipsets. If
&os; boots with a <errorname>failed with error 19</errorname>
message, disable xHCI/USB3 in the system
<acronym>BIOS</acronym>.</para>
</note>
<para>Support for <acronym>USB</acronym> storage devices is built
into the <filename>GENERIC</filename> kernel. For a custom
kernel, be sure that the following lines are present in the
kernel configuration file:</para>
<programlisting>device scbus # SCSI bus (required for ATA/SCSI)
device da # Direct Access (disks)
device pass # Passthrough device (direct ATA/SCSI access)
device uhci # provides USB 1.x support
device ohci # provides USB 1.x support
device ehci # provides USB 2.0 support
device xhci # provides USB 3.0 support
device usb # USB Bus (required)
device umass # Disks/Mass storage - Requires scbus and da
device cd # needed for CD and DVD burners</programlisting>
<para>&os; uses the &man.umass.4; driver which uses the
<acronym>SCSI</acronym> subsystem to access
<acronym>USB</acronym> storage devices. Since any
<acronym>USB</acronym> device will be seen as a
<acronym>SCSI</acronym> device by the system, if the
<acronym>USB</acronym> device is a <acronym>CD</acronym> or
<acronym>DVD</acronym> burner, do <emphasis>not</emphasis>
include <option>device atapicam</option> in a custom kernel
configuration file.</para>
<para>The rest of this section demonstrates how to verify that a
<acronym>USB</acronym> storage device is recognized by &os; and
how to configure the device so that it can be used.</para>
<sect2>
<title>Device Configuration</title>
<para>To test the <acronym>USB</acronym> configuration, plug in
the <acronym>USB</acronym> device. Use
<command>dmesg</command> to confirm that the drive appears in
the system message buffer. It should look something like
this:</para>
<screen>umass0: &lt;STECH Simple Drive, class 0/0, rev 2.00/1.04, addr 3&gt; on usbus0
umass0: SCSI over Bulk-Only; quirks = 0x0100
umass0:4:0:-1: Attached to scbus4
da0 at umass-sim0 bus 0 scbus4 target 0 lun 0
da0: &lt;STECH Simple Drive 1.04&gt; Fixed Direct Access SCSI-4 device
da0: Serial Number WD-WXE508CAN263
da0: 40.000MB/s transfers
da0: 152627MB (312581808 512 byte sectors: 255H 63S/T 19457C)
da0: quirks=0x2&lt;NO_6_BYTE&gt;</screen>
<para>The brand, device node (<filename>da0</filename>), speed,
and size will differ according to the device.</para>
<para>Since the <acronym>USB</acronym> device is seen as a
<acronym>SCSI</acronym> one, <command>camcontrol</command> can
be used to list the <acronym>USB</acronym> storage devices
attached to the system:</para>
<screen>&prompt.root; <userinput>camcontrol devlist</userinput>
&lt;STECH Simple Drive 1.04&gt; at scbus4 target 0 lun 0 (pass3,da0)</screen>
<para>Alternately, <command>usbconfig</command> can be used to
list the device. Refer to &man.usbconfig.8; for more
information about this command.</para>
<screen>&prompt.root; <userinput>usbconfig</userinput>
ugen0.3: &lt;Simple Drive STECH&gt; at usbus0, cfg=0 md=HOST spd=HIGH (480Mbps) pwr=ON (2mA)</screen>
<para>If the device has not been formatted, refer to <xref
linkend="disks-adding"/> for instructions on how to format
and create partitions on the <acronym>USB</acronym> drive. If
the drive comes with a file system, it can be mounted by
<systemitem class="username">root</systemitem> using the
instructions in <xref linkend="mount-unmount"/>.</para>
<warning>
<para>Allowing untrusted users to mount arbitrary media, by
enabling <varname>vfs.usermount</varname> as described
below, should not be considered safe from a security point
of view. Most file systems were not built to safeguard
against malicious devices.</para>
</warning>
<para>To make the device mountable as a normal user, one
solution is to make all users of the device a member of the
<systemitem class="groupname">operator</systemitem> group
using &man.pw.8;. Next, ensure that <systemitem
class="groupname">operator</systemitem> is able to read and
write the device by adding these lines to
<filename>/etc/devfs.rules</filename>:</para>
<programlisting>[localrules=5]
add path 'da*' mode 0660 group operator</programlisting>
<note>
<para>If internal <acronym>SCSI</acronym> disks are also
installed in the system, change the second line as
follows:</para>
<programlisting>add path 'da[<replaceable>3</replaceable>-9]*' mode 0660 group operator</programlisting>
<para>This will exclude the first three
<acronym>SCSI</acronym> disks (<filename>da0</filename> to
<filename>da2</filename>)from belonging to the <systemitem
class="groupname">operator</systemitem> group. Replace
<replaceable>3</replaceable> with the number of internal
<acronym>SCSI</acronym> disks. Refer to &man.devfs.rules.5;
for more information about this file.</para>
</note>
<para>Next, enable the ruleset in
<filename>/etc/rc.conf</filename>:</para>
<programlisting>devfs_system_ruleset="localrules"</programlisting>
<para>Then, instruct the system to allow regular users to mount
file systems by adding the following line to
<filename>/etc/sysctl.conf</filename>:</para>
<programlisting>vfs.usermount=1</programlisting>
<para>Since this only takes effect after the next reboot, use
<command>sysctl</command> to set this variable now:</para>
<screen>&prompt.root; <userinput>sysctl vfs.usermount=1</userinput>
vfs.usermount: 0 -&gt; 1</screen>
<para>The final step is to create a directory where the file
system is to be mounted. This directory needs to be owned by
the user that is to mount the file system. One way to do that
is for <systemitem class="username">root</systemitem> to
create a subdirectory owned by that user as <filename
class="directory">/mnt/<replaceable>username</replaceable></filename>.
In the following example, replace
<replaceable>username</replaceable> with the login name of the
user and <replaceable>usergroup</replaceable> with the user's
primary group:</para>
<screen>&prompt.root; <userinput>mkdir /mnt/<replaceable>username</replaceable></userinput>
&prompt.root; <userinput>chown <replaceable>username</replaceable>:<replaceable>usergroup</replaceable> /mnt/<replaceable>username</replaceable></userinput></screen>
<para>Suppose a <acronym>USB</acronym> thumbdrive is plugged in,
and a device <filename>/dev/da0s1</filename> appears. If the
device is formatted with a <acronym>FAT</acronym> file system,
the user can mount it using:</para>
<screen>&prompt.user; <userinput>mount -t msdosfs -o -m=644,-M=755 /dev/da0s1 /mnt/<replaceable>username</replaceable></userinput></screen>
<para>Before the device can be unplugged, it
<emphasis>must</emphasis> be unmounted first:</para>
<screen>&prompt.user; <userinput>umount /mnt/<replaceable>username</replaceable></userinput></screen>
<para>After device removal, the system message buffer will show
messages similar to the following:</para>
<screen>umass0: at uhub3, port 2, addr 3 (disconnected)
da0 at umass-sim0 bus 0 scbus4 target 0 lun 0
da0: &lt;STECH Simple Drive 1.04&gt; s/n WD-WXE508CAN263 detached
(da0:umass-sim0:0:0:0): Periph destroyed</screen>
</sect2>
</sect1>
<sect1 xml:id="creating-cds">
<info>
<title>Creating and Using <acronym>CD</acronym> Media</title>
<authorgroup>
<author>
<personname>
<firstname>Mike</firstname>
<surname>Meyer</surname>
</personname>
<contrib>Contributed by </contrib>
</author>
</authorgroup>
</info>
<indexterm>
<primary><acronym>CD-ROM</acronym>s</primary>
<secondary>creating</secondary>
</indexterm>
<para>Compact Disc (<acronym>CD</acronym>) media provide a number
of features that differentiate them from conventional disks.
They are designed so that they can be read continuously without
delays to move the head between tracks. While
<acronym>CD</acronym> media do have tracks, these refer to a
section of data to be read continuously, and not a physical
property of the disk. The <acronym>ISO</acronym> 9660 file
system was designed to deal with these differences.</para>
<indexterm><primary><acronym>ISO</acronym>
9660</primary></indexterm>
<indexterm>
<primary>file systems</primary>
<secondary>ISO 9660</secondary>
</indexterm>
<indexterm>
<primary><acronym>CD</acronym> burner</primary>
<secondary><acronym>ATAPI</acronym></secondary>
</indexterm>
<para>The &os; Ports Collection provides several utilities for
burning and duplicating audio and data <acronym>CD</acronym>s.
This chapter demonstrates the use of several command line
utilities. For <acronym>CD</acronym> burning software with a
graphical utility, consider installing the
<package>sysutils/xcdroast</package> or
<package>sysutils/k3b</package> packages or ports.</para>
<sect2 xml:id="atapicam">
<info>
<title>Supported Devices</title>
<authorgroup>
<author>
<personname>
<firstname>Marc</firstname>
<surname>Fonvieille</surname>
</personname>
<contrib>Contributed by </contrib>
</author>
</authorgroup>
</info>
<indexterm>
<primary><acronym>CD</acronym> burner</primary>
<secondary>ATAPI/CAM driver</secondary>
</indexterm>
<para>The <filename>GENERIC</filename> kernel provides support
for <acronym>SCSI</acronym>, <acronym>USB</acronym>, and
<acronym>ATAPI</acronym> <acronym>CD</acronym> readers and
burners. If a custom kernel is used, the options that need to
be present in the kernel configuration file vary by the type
of device.</para>
<para>For a <acronym>SCSI</acronym> burner, make sure these
options are present:</para>
<programlisting>device scbus # SCSI bus (required for ATA/SCSI)
device da # Direct Access (disks)
device pass # Passthrough device (direct ATA/SCSI access)
device cd # needed for CD and DVD burners</programlisting>
<para>For a <acronym>USB</acronym> burner, make sure these
options are present:</para>
<programlisting>device scbus # SCSI bus (required for ATA/SCSI)
device da # Direct Access (disks)
device pass # Passthrough device (direct ATA/SCSI access)
device cd # needed for CD and DVD burners
device uhci # provides USB 1.x support
device ohci # provides USB 1.x support
device ehci # provides USB 2.0 support
device xhci # provides USB 3.0 support
device usb # USB Bus (required)
device umass # Disks/Mass storage - Requires scbus and da</programlisting>
<para>For an <acronym>ATAPI</acronym> burner, make sure these
options are present:</para>
<programlisting>device ata # Legacy ATA/SATA controllers
device scbus # SCSI bus (required for ATA/SCSI)
device pass # Passthrough device (direct ATA/SCSI access)
device cd # needed for CD and DVD burners</programlisting>
<note>
<para>On &os; versions prior to 10.x, this line is also
needed in the kernel configuration file if the burner is an
<acronym>ATAPI</acronym> device:</para>
<programlisting>device atapicam</programlisting>
<para>Alternately, this driver can be loaded at boot time by
adding the following line to
<filename>/boot/loader.conf</filename>:</para>
<programlisting>atapicam_load="YES"</programlisting>
<para>This will require a reboot of the system as this driver
can only be loaded at boot time.</para>
</note>
<para>To verify that &os; recognizes the device, run
<command>dmesg</command> and look for an entry for the device.
On systems prior to 10.x, the device name in the first line of
the output will be <filename>acd0</filename> instead of
<filename>cd0</filename>.</para>
<screen>&prompt.user; <userinput>dmesg | grep cd</userinput>
cd0 at ahcich1 bus 0 scbus1 target 0 lun 0
cd0: &lt;HL-DT-ST DVDRAM GU70N LT20&gt; Removable CD-ROM SCSI-0 device
cd0: Serial Number M3OD3S34152
cd0: 150.000MB/s transfers (SATA 1.x, UDMA6, ATAPI 12bytes, PIO 8192bytes)
cd0: Attempt to query device size failed: NOT READY, Medium not present - tray closed</screen>
</sect2>
<sect2 xml:id="cdrecord">
<title>Burning a <acronym>CD</acronym></title>
<para>In &os;, <command>cdrecord</command> can be used to burn
<acronym>CD</acronym>s. This command is installed with the
<package>sysutils/cdrtools</package> package or port.</para>
<note>
<para>&os; 8.x includes the built-in
<command>burncd</command> utility for burning
<acronym>CD</acronym>s using an <acronym>ATAPI</acronym>
<acronym>CD</acronym> burner. Refer to the manual page for
<command>burncd</command> for usage examples.</para>
</note>
<para>While <command>cdrecord</command> has many options, basic
usage is simple. Specify the name of the
<acronym>ISO</acronym> file to burn and, if the system has
multiple burner devices, specify the name of the device to
use:</para>
<screen>&prompt.root; <userinput>cdrecord <replaceable>dev=device</replaceable> <replaceable>imagefile.iso</replaceable></userinput></screen>
<para>To determine the device name of the burner, use
<option>-scanbus</option> which might produce results like
this:</para>
<indexterm>
<primary><acronym>CD-ROM</acronym>s</primary>
<secondary>burning</secondary>
</indexterm>
<screen>&prompt.root; <userinput>cdrecord -scanbus</userinput>
ProDVD-ProBD-Clone 3.00 (amd64-unknown-freebsd10.0) Copyright (C) 1995-2010 J&ouml;rg Schilling
Using libscg version 'schily-0.9'
scsibus0:
0,0,0 0) 'SEAGATE ' 'ST39236LW ' '0004' Disk
0,1,0 1) 'SEAGATE ' 'ST39173W ' '5958' Disk
0,2,0 2) *
0,3,0 3) 'iomega ' 'jaz 1GB ' 'J.86' Removable Disk
0,4,0 4) 'NEC ' 'CD-ROM DRIVE:466' '1.26' Removable CD-ROM
0,5,0 5) *
0,6,0 6) *
0,7,0 7) *
scsibus1:
1,0,0 100) *
1,1,0 101) *
1,2,0 102) *
1,3,0 103) *
1,4,0 104) *
1,5,0 105) 'YAMAHA ' 'CRW4260 ' '1.0q' Removable CD-ROM
1,6,0 106) 'ARTEC ' 'AM12S ' '1.06' Scanner
1,7,0 107) *</screen>
<para>Locate the entry for the <acronym>CD</acronym> burner and
use the three numbers separated by commas as the value for
<option>dev</option>. In this case, the Yamaha burner device
is <literal>1,5,0</literal>, so the appropriate input to
specify that device is <option>dev=1,5,0</option>. Refer to
the manual page for <command>cdrecord</command> for other ways
to specify this value and for information on writing audio
tracks and controlling the write speed.</para>
<para>Alternately, run the following command to get the device
address of the burner:</para>
<screen>&prompt.root; <userinput>camcontrol devlist</userinput>
&lt;MATSHITA CDRW/DVD UJDA740 1.00&gt; at scbus1 target 0 lun 0 (cd0,pass0)</screen>
<para>Use the numeric values for <literal>scbus</literal>,
<literal>target</literal>, and <literal>lun</literal>. For
this example, <literal>1,0,0</literal> is the device name to
use.</para>
</sect2>
<sect2 xml:id="mkisofs">
<title>Writing Data to an <acronym>ISO</acronym> File
System</title>
<para>In order to produce a data <acronym>CD</acronym>, the data
files that are going to make up the tracks on the
<acronym>CD</acronym> must be prepared before they can be
burned to the <acronym>CD</acronym>. In &os;,
<package>sysutils/cdrtools</package> installs
<command>mkisofs</command>, which can be used to produce an
<acronym>ISO</acronym> 9660 file system that is an image of a
directory tree within a &unix; file system. The simplest
usage is to specify the name of the <acronym>ISO</acronym>
file to create and the path to the files to place into the
<acronym>ISO</acronym> 9660 file system:</para>
<screen>&prompt.root; <userinput>mkisofs -o <replaceable>imagefile.iso</replaceable> <replaceable>/path/to/tree</replaceable></userinput></screen>
<indexterm>
<primary>file systems</primary>
<secondary>ISO 9660</secondary>
</indexterm>
<para>This command maps the file names in the specified path to
names that fit the limitations of the standard
<acronym>ISO</acronym> 9660 file system, and will exclude
files that do not meet the standard for <acronym>ISO</acronym>
file systems.</para>
<indexterm>
<primary>file systems</primary>
<secondary>Joliet</secondary>
</indexterm>
<para>A number of options are available to overcome the
restrictions imposed by the standard. In particular,
<option>-R</option> enables the Rock Ridge extensions common
to &unix; systems and <option>-J</option> enables Joliet
extensions used by &microsoft; systems.</para>
<para>For <acronym>CD</acronym>s that are going to be used only
on &os; systems, <option>-U</option> can be used to disable
all filename restrictions. When used with
<option>-R</option>, it produces a file system image that is
identical to the specified &os; tree, even if it violates the
<acronym>ISO</acronym> 9660 standard.</para>
<indexterm>
<primary><acronym>CD-ROM</acronym>s</primary>
<secondary>creating bootable</secondary>
</indexterm>
<para>The last option of general use is <option>-b</option>.
This is used to specify the location of a boot image for use
in producing an <quote>El Torito</quote> bootable
<acronym>CD</acronym>. This option takes an argument which is
the path to a boot image from the top of the tree being
written to the <acronym>CD</acronym>. By default,
<command>mkisofs</command> creates an <acronym>ISO</acronym>
image in <quote>floppy disk emulation</quote> mode, and thus
expects the boot image to be exactly 1200, 1440 or
2880&nbsp;KB in size. Some boot loaders, like the one used by
the &os; distribution media, do not use emulation mode. In
this case, <option>-no-emul-boot</option> should be used. So,
if <filename>/tmp/myboot</filename> holds a bootable &os;
system with the boot image in
<filename>/tmp/myboot/boot/cdboot</filename>, this command
would produce
<filename>/tmp/bootable.iso</filename>:</para>
<screen>&prompt.root; <userinput>mkisofs -R -no-emul-boot -b boot/cdboot -o /tmp/bootable.iso /tmp/myboot</userinput></screen>
<para>The resulting <acronym>ISO</acronym> image can be mounted
as a memory disk with:</para>
<screen>&prompt.root; <userinput>mdconfig -a -t vnode -f /tmp/bootable.iso -u 0</userinput>
&prompt.root; <userinput>mount -t cd9660 /dev/md0 /mnt</userinput></screen>
<para>One can then verify that <filename>/mnt</filename> and
<filename>/tmp/myboot</filename> are identical.</para>
<para>There are many other options available for
<command>mkisofs</command> to fine-tune its behavior. Refer
to &man.mkisofs.8; for details.</para>
<note>
<para>It is possible to copy a data <acronym>CD</acronym> to
an image file that is functionally equivalent to the image
file created with <command>mkisofs</command>. To do so, use
<filename>dd</filename> with the device name as the input
file and the name of the <acronym>ISO</acronym> to create as
the output file:</para>
<screen>&prompt.root; <userinput>dd if=/dev/<replaceable>cd0</replaceable> of=<replaceable>file.iso</replaceable> bs=2048</userinput></screen>
<para>The resulting image file can be burned to
<acronym>CD</acronym> as described in <xref
linkend="cdrecord"/>.</para>
</note>
</sect2>
<sect2 xml:id="mounting-cd">
<title>Using Data <acronym>CD</acronym>s</title>
<para>Once an <acronym>ISO</acronym> has been burned to a
<acronym>CD</acronym>, it can be mounted by specifying the
file system type, the name of the device containing the
<acronym>CD</acronym>, and an existing mount point:</para>
<screen>&prompt.root; <userinput>mount -t cd9660 <replaceable>/dev/cd0</replaceable> <replaceable>/mnt</replaceable></userinput></screen>
<para>Since <command>mount</command> assumes that a file system
is of type <literal>ufs</literal>, a <errorname>Incorrect
super block</errorname> error will occur if <literal>-t
cd9660</literal> is not included when mounting a data
<acronym>CD</acronym>.</para>
<para>While any data <acronym>CD</acronym> can be mounted this
way, disks with certain <acronym>ISO</acronym> 9660 extensions
might behave oddly. For example, Joliet disks store all
filenames in two-byte Unicode characters. If some non-English
characters show up as question marks, specify the local
charset with <option>-C</option>. For more information, refer
to &man.mount.cd9660.8;.</para>
<note>
<para>In order to do this character conversion with the help
of <option>-C</option>, the kernel requires the
<filename>cd9660_iconv.ko</filename> module to be loaded.
This can be done either by adding this line to
<filename>loader.conf</filename>:</para>
<programlisting>cd9660_iconv_load="YES"</programlisting>
<para>and then rebooting the machine, or by directly loading
the module with <command>kldload</command>.</para>
</note>
<para>Occasionally, <errorname>Device not configured</errorname>
will be displayed when trying to mount a data
<acronym>CD</acronym>. This usually means that the
<acronym>CD</acronym> drive thinks that there is no disk in
the tray, or that the drive is not visible on the bus. It
can take a couple of seconds for a <acronym>CD</acronym>
drive to realize that a media is present, so be
patient.</para>
<para>Sometimes, a <acronym>SCSI</acronym>
<acronym>CD</acronym> drive may be missed because it did not
have enough time to answer the bus reset. To resolve this,
a custom kernel can be created which increases the default
<acronym>SCSI</acronym> delay. Add the following option to
the custom kernel configuration file and rebuild the kernel
using the instructions in <xref
linkend="kernelconfig-building"/>:</para>
<programlisting>options SCSI_DELAY=15000</programlisting>
<para>This tells the <acronym>SCSI</acronym> bus to pause 15
seconds during boot, to give the <acronym>CD</acronym>
drive every possible chance to answer the bus reset.</para>
<note>
<para>It is possible to burn a file directly to
<acronym>CD</acronym>, without creating an
<acronym>ISO</acronym> 9660 file system. This is known as
burning a raw data <acronym>CD</acronym> and some people do
this for backup purposes.</para>
<para>This type of disk can not be mounted as a normal data
<acronym>CD</acronym>. In order to retrieve the data burned
to such a <acronym>CD</acronym>, the data must be read from
the raw device node. For example, this command will extract
a compressed tar file located on the second
<acronym>CD</acronym> device into the current working
directory:</para>
<screen>&prompt.root; <userinput>tar xzvf /dev/<replaceable>cd1</replaceable></userinput></screen>
<para> In order to mount a data <acronym>CD</acronym>, the
data must be written using
<command>mkisofs</command>.</para>
</note>
</sect2>
<sect2 xml:id="duplicating-audiocds">
<title>Duplicating Audio <acronym>CD</acronym>s</title>
<para>To duplicate an audio <acronym>CD</acronym>, extract the
audio data from the <acronym>CD</acronym> to a series of
files, then write these files to a blank
<acronym>CD</acronym>.</para>
<para><xref linkend="using-cdrecord"/> describes how to
duplicate and burn an audio <acronym>CD</acronym>. If the
&os; version is less than 10.0 and the device is
<acronym>ATAPI</acronym>, the <option>atapicam</option> module
must be first loaded using the instructions in <xref
linkend="atapicam"/>.</para>
<procedure xml:id="using-cdrecord">
<title>Duplicating an Audio <acronym>CD</acronym></title>
<step>
<para>The <package>sysutils/cdrtools</package> package or
port installs <command>cdda2wav</command>. This command
can be used to extract all of the audio tracks, with each
track written to a separate <acronym>WAV</acronym> file in
the current working directory:</para>
<screen>&prompt.user; <userinput>cdda2wav -vall -B -Owav</userinput></screen>
<para>A device name does not need to be specified if there
is only one <acronym>CD</acronym> device on the system.
Refer to the <command>cdda2wav</command> manual page for
instructions on how to specify a device and to learn more
about the other options available for this command.</para>
</step>
<step>
<para>Use <command>cdrecord</command> to write the
<filename>.wav</filename> files:</para>
<screen>&prompt.user; <userinput>cdrecord -v dev=<replaceable>2,0</replaceable> -dao -useinfo *.wav</userinput></screen>
<para>Make sure that <replaceable>2,0</replaceable> is set
appropriately, as described in <xref
linkend="cdrecord"/>.</para>
</step>
</procedure>
</sect2>
</sect1>
<sect1 xml:id="creating-dvds">
<info>
<title>Creating and Using <acronym>DVD</acronym> Media</title>
<authorgroup>
<author>
<personname>
<firstname>Marc</firstname>
<surname>Fonvieille</surname>
</personname>
<contrib>Contributed by </contrib>
</author>
</authorgroup>
<authorgroup>
<author>
<personname>
<firstname>Andy</firstname>
<surname>Polyakov</surname>
</personname>
<contrib>With inputs from </contrib>
</author>
</authorgroup>
</info>
<indexterm>
<primary><acronym>DVD</acronym></primary>
<secondary>burning</secondary>
</indexterm>
<para>Compared to the <acronym>CD</acronym>, the
<acronym>DVD</acronym> is the next generation of optical media
storage technology. The <acronym>DVD</acronym> can hold more
data than any <acronym>CD</acronym> and is the standard for
video publishing.</para>
<para>Five physical recordable formats can be defined for a
recordable <acronym>DVD</acronym>:</para>
<itemizedlist>
<listitem>
<para>DVD-R: This was the first <acronym>DVD</acronym>
recordable format available. The DVD-R standard is defined
by the <link
xlink:href="http://www.dvdforum.com/forum.shtml"><acronym>DVD</acronym>
Forum</link>. This format is write once.</para>
</listitem>
<listitem>
<para><acronym>DVD-RW</acronym>: This is the rewritable
version of the DVD-R standard. A
<acronym>DVD-RW</acronym> can be rewritten about 1000
times.</para>
</listitem>
<listitem>
<para><acronym>DVD-RAM</acronym>: This is a rewritable format
which can be seen as a removable hard drive. However, this
media is not compatible with most
<acronym>DVD-ROM</acronym> drives and DVD-Video players as
only a few <acronym>DVD</acronym> writers support the
<acronym>DVD-RAM</acronym> format. Refer to <xref
linkend="creating-dvd-ram"/> for more information on
<acronym>DVD-RAM</acronym> use.</para>
</listitem>
<listitem>
<para><acronym>DVD+RW</acronym>: This is a rewritable format
defined by the <link
xlink:href="http://www.dvdrw.com/"><acronym>DVD+RW</acronym>
Alliance</link>. A <acronym>DVD+RW</acronym> can be
rewritten about 1000 times.</para>
</listitem>
<listitem>
<para>DVD+R: This format is the write once variation of the
<acronym>DVD+RW</acronym> format.</para>
</listitem>
</itemizedlist>
<para>A single layer recordable <acronym>DVD</acronym> can hold up
to 4,700,000,000&nbsp;bytes which is actually 4.38&nbsp;GB or
4485&nbsp;MB as 1 kilobyte is 1024 bytes.</para>
<note>
<para>A distinction must be made between the physical media and
the application. For example, a DVD-Video is a specific file
layout that can be written on any recordable
<acronym>DVD</acronym> physical media such as DVD-R, DVD+R, or
<acronym>DVD-RW</acronym>. Before choosing the type of media,
ensure that both the burner and the DVD-Video player are
compatible with the media under consideration.</para>
</note>
<sect2>
<title>Configuration</title>
<para>To perform <acronym>DVD</acronym> recording, use
&man.growisofs.1;. This command is part of the
<package>sysutils/dvd+rw-tools</package> utilities which
support all <acronym>DVD</acronym> media types.</para>
<para>These tools use the <acronym>SCSI</acronym> subsystem to
access the devices, therefore <link
linkend="atapicam">ATAPI/CAM support</link> must be loaded
or statically compiled into the kernel. This support is not
needed if the burner uses the <acronym>USB</acronym>
interface. Refer to <xref linkend="usb-disks"/> for more
details on <acronym>USB</acronym> device configuration.</para>
<para>DMA access must also be enabled for
<acronym>ATAPI</acronym> devices, by adding the following line
to <filename>/boot/loader.conf</filename>:</para>
<programlisting>hw.ata.atapi_dma="1"</programlisting>
<para>Before attempting to use
<application>dvd+rw-tools</application>, consult the <link
xlink:href="http://fy.chalmers.se/~appro/linux/DVD+RW/hcn.html">Hardware
Compatibility Notes</link>.</para>
<note>
<para>For a graphical user interface, consider using
<package>sysutils/k3b</package> which provides a user
friendly interface to &man.growisofs.1; and many other
burning tools.</para>
</note>
</sect2>
<sect2>
<title>Burning Data <acronym>DVD</acronym>s</title>
<para>Since &man.growisofs.1; is a front-end to <link
linkend="mkisofs">mkisofs</link>, it will invoke
&man.mkisofs.8; to create the file system layout and perform
the write on the <acronym>DVD</acronym>. This means that an
image of the data does not need to be created before the
burning process.</para>
<para>To burn to a DVD+R or a DVD-R the data in
<filename>/path/to/data</filename>, use the following
command:</para>
<screen>&prompt.root; <userinput>growisofs -dvd-compat -Z <replaceable>/dev/cd0</replaceable> -J -R <replaceable>/path/to/data</replaceable></userinput></screen>
<para>In this example, <option>-J -R</option> is passed to
&man.mkisofs.8; to create an ISO 9660 file system with Joliet
and Rock Ridge extensions. Refer to &man.mkisofs.8; for more
details.</para>
<para>For the initial session recording, <option>-Z</option> is
used for both single and multiple sessions. Replace
<replaceable>/dev/cd0</replaceable>, with the name of the
<acronym>DVD</acronym> device. Using
<option>-dvd-compat</option> indicates that the disk will be
closed and that the recording will be unappendable. This
should also provide better media compatibility with
<acronym>DVD-ROM</acronym> drives.</para>
<para>To burn a pre-mastered image, such as
<replaceable>imagefile.iso</replaceable>, use:</para>
<screen>&prompt.root; <userinput>growisofs -dvd-compat -Z <replaceable>/dev/cd0</replaceable>=<replaceable>imagefile.iso</replaceable></userinput></screen>
<para>The write speed should be detected and automatically set
according to the media and the drive being used. To force the
write speed, use <option>-speed=</option>. Refer to
&man.growisofs.1; for example usage.</para>
<note>
<para>In order to support working files larger than 4.38GB, an
UDF/ISO-9660 hybrid file system must be created by passing
<option>-udf -iso-level 3</option> to &man.mkisofs.8; and
all related programs, such as &man.growisofs.1;. This is
required only when creating an ISO image file or when
writing files directly to a disk. Since a disk created this
way must be mounted as an UDF file system with
&man.mount.udf.8;, it will be usable only on an UDF aware
operating system. Otherwise it will look as if it contains
corrupted files.</para>
<para>To create this type of ISO file:</para>
<screen>&prompt.user; <userinput>mkisofs -R -J -udf -iso-level 3 -o <replaceable>imagefile.iso</replaceable> <replaceable>/path/to/data</replaceable></userinput></screen>
<para>To burn files directly to a disk:</para>
<screen>&prompt.root; <userinput>growisofs -dvd-compat -udf -iso-level 3 -Z <replaceable>/dev/cd0</replaceable> -J -R <replaceable>/path/to/data</replaceable></userinput></screen>
<para>When an ISO image already contains large files, no
additional options are required for &man.growisofs.1; to
burn that image on a disk.</para>
<para>Be sure to use an up-to-date version of
<package>sysutils/cdrtools</package>, which contains
&man.mkisofs.8;, as an older version may not contain large
files support. If the latest version does not work, install
<package>sysutils/cdrtools-devel</package> and read its
&man.mkisofs.8;.</para>
</note>
</sect2>
<sect2>
<title>Burning a <acronym>DVD</acronym>-Video</title>
<indexterm>
<primary><acronym>DVD</acronym></primary>
<secondary>DVD-Video</secondary>
</indexterm>
<para>A DVD-Video is a specific file layout based on the ISO
9660 and micro-UDF (M-UDF) specifications. Since DVD-Video
presents a specific data structure hierarchy, a particular
program such as <package>multimedia/dvdauthor</package> is
needed to author the <acronym>DVD</acronym>.</para>
<para>If an image of the DVD-Video file system already exists,
it can be burned in the same way as any other image. If
<command>dvdauthor</command> was used to make the
<acronym>DVD</acronym> and the result is in
<filename>/path/to/video</filename>, the following command
should be used to burn the DVD-Video:</para>
<screen>&prompt.root; <userinput>growisofs -Z <replaceable>/dev/cd0</replaceable> -dvd-video <replaceable>/path/to/video</replaceable></userinput></screen>
<para><option>-dvd-video</option> is passed to &man.mkisofs.8;
to instruct it to create a DVD-Video file system layout.
This option implies the <option>-dvd-compat</option>
&man.growisofs.1; option.</para>
</sect2>
<sect2>
<title>Using a <acronym>DVD+RW</acronym></title>
<indexterm>
<primary><acronym>DVD</acronym></primary>
<secondary><acronym>DVD+RW</acronym></secondary>
</indexterm>
<para>Unlike CD-RW, a virgin <acronym>DVD+RW</acronym> needs to
be formatted before first use. It is
<emphasis>recommended</emphasis> to let &man.growisofs.1; take
care of this automatically whenever appropriate. However, it
is possible to use <command>dvd+rw-format</command> to format
the <acronym>DVD+RW</acronym>:</para>
<screen>&prompt.root; <userinput>dvd+rw-format <replaceable>/dev/cd0</replaceable></userinput></screen>
<para>Only perform this operation once and keep in mind that
only virgin <acronym>DVD+RW</acronym> medias need to be
formatted. Once formatted, the <acronym>DVD+RW</acronym> can
be burned as usual.</para>
<para>To burn a totally new file system and not just append some
data onto a <acronym>DVD+RW</acronym>, the media does not need
to be blanked first. Instead, write over the previous
recording like this:</para>
<screen>&prompt.root; <userinput>growisofs -Z <replaceable>/dev/cd0</replaceable> -J -R <replaceable>/path/to/newdata</replaceable></userinput></screen>
<para>The <acronym>DVD+RW</acronym> format supports appending
data to a previous recording. This operation consists of
merging a new session to the existing one as it is not
considered to be multi-session writing. &man.growisofs.1;
will <emphasis>grow</emphasis> the ISO 9660 file system
present on the media.</para>
<para>For example, to append data to a
<acronym>DVD+RW</acronym>, use the following:</para>
<screen>&prompt.root; <userinput>growisofs -M <replaceable>/dev/cd0</replaceable> -J -R <replaceable>/path/to/nextdata</replaceable></userinput></screen>
<para>The same &man.mkisofs.8; options used to burn the
initial session should be used during next writes.</para>
<note>
<para>Use <option>-dvd-compat</option> for better media
compatibility with <acronym>DVD-ROM</acronym> drives. When
using <acronym>DVD+RW</acronym>, this option will not
prevent the addition of data.</para>
</note>
<para>To blank the media, use:</para>
<screen>&prompt.root; <userinput>growisofs -Z <replaceable>/dev/cd0</replaceable>=<replaceable>/dev/zero</replaceable></userinput></screen>
</sect2>
<sect2>
<title>Using a <acronym>DVD-RW</acronym></title>
<indexterm>
<primary><acronym>DVD</acronym></primary>
<secondary><acronym>DVD-RW</acronym></secondary>
</indexterm>
<para>A <acronym>DVD-RW</acronym> accepts two disc formats:
incremental sequential and restricted overwrite. By default,
<acronym>DVD-RW</acronym> discs are in sequential
format.</para>
<para>A virgin <acronym>DVD-RW</acronym> can be directly written
without being formatted. However, a non-virgin
<acronym>DVD-RW</acronym> in sequential format needs to be
blanked before writing a new initial session.</para>
<para>To blank a <acronym>DVD-RW</acronym> in sequential
mode:</para>
<screen>&prompt.root; <userinput>dvd+rw-format -blank=full <replaceable>/dev/cd0</replaceable></userinput></screen>
<note>
<para>A full blanking using <option>-blank=full</option> will
take about one hour on a 1x media. A fast blanking can be
performed using <option>-blank</option>, if the
<acronym>DVD-RW</acronym> will be recorded in Disk-At-Once
(DAO) mode. To burn the <acronym>DVD-RW</acronym> in DAO
mode, use the command:</para>
<screen>&prompt.root; <userinput>growisofs -use-the-force-luke=dao -Z <replaceable>/dev/cd0</replaceable>=<replaceable>imagefile.iso</replaceable></userinput></screen>
<para>Since &man.growisofs.1; automatically attempts to detect
fast blanked media and engage DAO write,
<option>-use-the-force-luke=dao</option> should not be
required.</para>
<para>One should instead use restricted overwrite mode with
any <acronym>DVD-RW</acronym> as this format is more
flexible than the default of incremental sequential.</para>
</note>
<para>To write data on a sequential <acronym>DVD-RW</acronym>,
use the same instructions as for the other
<acronym>DVD</acronym> formats:</para>
<screen>&prompt.root; <userinput>growisofs -Z <replaceable>/dev/cd0</replaceable> -J -R <replaceable>/path/to/data</replaceable></userinput></screen>
<para>To append some data to a previous recording, use
<option>-M</option> with &man.growisofs.1;. However, if data
is appended on a <acronym>DVD-RW</acronym> in incremental
sequential mode, a new session will be created on the disc and
the result will be a multi-session disc.</para>
<para>A <acronym>DVD-RW</acronym> in restricted overwrite format
does not need to be blanked before a new initial session.
Instead, overwrite the disc with <option>-Z</option>. It is
also possible to grow an existing ISO 9660 file system written
on the disc with <option>-M</option>. The result will be a
one-session <acronym>DVD</acronym>.</para>
<para>To put a <acronym>DVD-RW</acronym> in restricted overwrite
format, the following command must be used:</para>
<screen>&prompt.root; <userinput>dvd+rw-format <replaceable>/dev/cd0</replaceable></userinput></screen>
<para>To change back to sequential format, use:</para>
<screen>&prompt.root; <userinput>dvd+rw-format -blank=full <replaceable>/dev/cd0</replaceable></userinput></screen>
</sect2>
<sect2>
<title>Multi-Session</title>
<para>Few <acronym>DVD-ROM</acronym> drives support
multi-session DVDs and most of the time only read the first
session. DVD+R, DVD-R and <acronym>DVD-RW</acronym> in
sequential format can accept multiple sessions. The notion
of multiple sessions does not exist for the
<acronym>DVD+RW</acronym> and the <acronym>DVD-RW</acronym>
restricted overwrite formats.</para>
<para>Using the following command after an initial non-closed
session on a DVD+R, DVD-R, or <acronym>DVD-RW</acronym> in
sequential format, will add a new session to the disc:</para>
<screen>&prompt.root; <userinput>growisofs -M <replaceable>/dev/cd0</replaceable> -J -R <replaceable>/path/to/nextdata</replaceable></userinput></screen>
<para>Using this command with a <acronym>DVD+RW</acronym> or a
<acronym>DVD-RW</acronym> in restricted overwrite mode will
append data while merging the new session to the existing one.
The result will be a single-session disc. Use this method to
add data after an initial write on these types of
media.</para>
<note>
<para>Since some space on the media is used between each
session to mark the end and start of sessions, one should
add sessions with a large amount of data to optimize media
space. The number of sessions is limited to 154 for a
DVD+R, about 2000 for a DVD-R, and 127 for a DVD+R Double
Layer.</para>
</note>
</sect2>
<sect2>
<title>For More Information</title>
<para>To obtain more information about a <acronym>DVD</acronym>,
use <command>dvd+rw-mediainfo
<replaceable>/dev/cd0</replaceable></command> while the
disc in the specified drive.</para>
<para>More information about
<application>dvd+rw-tools</application> can be found in
&man.growisofs.1;, on the <link
xlink:href="http://fy.chalmers.se/~appro/linux/DVD+RW/">dvd+rw-tools
web site</link>, and in the <link
xlink:href="http://lists.debian.org/cdwrite/">cdwrite
mailing list</link> archives.</para>
<note>
<para>When creating a problem report related to the use of
<application>dvd+rw-tools</application>, always include the
output of <command>dvd+rw-mediainfo</command>.</para>
</note>
</sect2>
<sect2 xml:id="creating-dvd-ram">
<title>Using a <acronym>DVD-RAM</acronym></title>
<indexterm>
<primary><acronym>DVD</acronym></primary>
<secondary><acronym>DVD-RAM</acronym></secondary>
</indexterm>
<para><acronym>DVD-RAM</acronym> writers can use either a
<acronym>SCSI</acronym> or <acronym>ATAPI</acronym> interface.
For <acronym>ATAPI</acronym> devices, DMA access has to be
enabled by adding the following line to
<filename>/boot/loader.conf</filename>:</para>
<programlisting>hw.ata.atapi_dma="1"</programlisting>
<para>A <acronym>DVD-RAM</acronym> can be seen as a removable
hard drive. Like any other hard drive, the
<acronym>DVD-RAM</acronym> must be formatted before it can be
used. In this example, the whole disk space will be formatted
with a standard UFS2 file system:</para>
<screen>&prompt.root; <userinput>dd if=/dev/zero of=<replaceable>/dev/acd0</replaceable> bs=2k count=1</userinput>
&prompt.root; <userinput>bsdlabel -Bw <replaceable>acd0</replaceable></userinput>
&prompt.root; <userinput>newfs <replaceable>/dev/acd0</replaceable></userinput></screen>
<para>The <acronym>DVD</acronym> device,
<filename>acd0</filename>, must be changed according to the
configuration.</para>
<para>Once the <acronym>DVD-RAM</acronym> has been formatted, it
can be mounted as a normal hard drive:</para>
<screen>&prompt.root; <userinput>mount <replaceable>/dev/acd0</replaceable> <replaceable>/mnt</replaceable></userinput></screen>
<para>Once mounted, the <acronym>DVD-RAM</acronym> will be both
readable and writeable.</para>
</sect2>
</sect1>
<sect1 xml:id="floppies">
<title>Creating and Using Floppy Disks</title>
<!--
<authorgroup>
<author>
<personname>
<firstname>Julio</firstname>
<surname>Merino</surname>
</personname>
<contrib>Original work by </contrib>
</author>
</authorgroup>
<authorgroup>
<author>
<personname>
<firstname>Martin</firstname>
<surname>Karlsson</surname>
</personname>
<contrib>Rewritten by </contrib>
</author>
</authorgroup>
-->
<para>This section explains how to format a 3.5 inch floppy disk
in &os;.</para>
<procedure>
<title>Steps to Format a Floppy</title>
<para>A floppy disk needs to be low-level formatted before it
can be used. This is usually done by the vendor, but
formatting is a good way to check media integrity. To
low-level format the floppy disk on &os;, use
&man.fdformat.1;. When using this utility, make note of any
error messages, as these can help determine if the disk is
good or bad.</para>
<step>
<para>To format the floppy, insert a new 3.5 inch floppy disk
into the first floppy drive and issue:</para>
<screen>&prompt.root; <userinput>/usr/sbin/fdformat -f 1440 /dev/fd0</userinput></screen>
</step>
<step>
<para>After low-level formatting the disk, create a disk label
as it is needed by the system to determine the size of the
disk and its geometry. The supported geometry values are
listed in <filename>/etc/disktab</filename>.</para>
<para>To write the disk label, use &man.bsdlabel.8;:</para>
<screen>&prompt.root; <userinput>/sbin/bsdlabel -B -w /dev/fd0 fd1440</userinput></screen>
</step>
<step>
<para>The floppy is now ready to be high-level formatted with
a file system. The floppy's file system can be either UFS
or FAT, where FAT is generally a better choice for
floppies.</para>
<para>To format the floppy with FAT, issue:</para>
<screen>&prompt.root; <userinput>/sbin/newfs_msdos /dev/fd0</userinput></screen>
</step>
</procedure>
<para>The disk is now ready for use. To use the floppy, mount it
with &man.mount.msdosfs.8;. One can also install and use
<package>emulators/mtools</package> from the Ports
Collection.</para>
</sect1>
<sect1 xml:id="backup-basics">
<title>Backup Basics</title>
<!--
<authorgroup>
<author>
<personname>
<firstname>Lowell</firstname>
<surname>Gilbert</surname>
</personname>
<contrib>Original work by </contrib>
</author>
</authorgroup>
-->
<para>Implementing a backup plan is essential in order to have the
ability to recover from disk failure, accidental file deletion,
random file corruption, or complete machine destruction,
including destruction of on-site backups.</para>
<para>The backup type and schedule will vary, depending upon the
importance of the data, the granularity needed for file
restores, and the amount of acceptable downtime. Some possible
backup techniques include:</para>
<itemizedlist>
<listitem>
<para>Archives of the whole system, backed up onto permanent,
off-site media. This provides protection against all of the
problems listed above, but is slow and inconvenient to
restore from, especially for non-privileged users.</para>
</listitem>
<listitem>
<para>File system snapshots, which are useful for restoring
deleted files or previous versions of files.</para>
</listitem>
<listitem>
<para>Copies of whole file systems or disks which are
sychronized with another system on the network using a
scheduled <package>net/rsync</package>.</para>
</listitem>
<listitem>
<para>Hardware or software <acronym>RAID</acronym>, which
minimizes or avoids downtime when a disk fails.</para>
</listitem>
</itemizedlist>
<para>Typically, a mix of backup techniques is used. For
example, one could create a schedule to automate a weekly, full
system backup that is stored off-site and to supplement this
backup with hourly ZFS snapshots. In addition, one could make a
manual backup of individual directories or files before making
file edits or deletions.</para>
<para>This section describes some of the utilities which can be
used to create and manage backups on a &os; system.</para>
<sect2>
<title>File System Backups</title>
<indexterm>
<primary>backup software</primary>
<secondary>dump / restore</secondary>
</indexterm>
<indexterm>
<primary><command>dump</command></primary>
</indexterm>
<indexterm>
<primary><command>restore</command></primary>
</indexterm>
<para>The traditional &unix; programs for backing up a file
system are &man.dump.8;, which creates the backup, and
&man.restore.8;, which restores the backup. These utilities
work at the disk block level, below the abstractions of the
files, links, and directories that are created by file
systems. Unlike other backup software,
<command>dump</command> backs up an entire file system and is
unable to backup only part of a file system or a directory
tree that spans multiple file systems. Instead of writing
files and directories, <command>dump</command> writes the raw
data blocks that comprise files and directories.</para>
<note>
<para>If <command>dump</command> is used on the root
directory, it will not back up <filename>/home</filename>,
<filename>/usr</filename> or many other directories since
these are typically mount points for other file systems or
symbolic links into those file systems.</para>
</note>
<para>When used to restore data, <command>restore</command>
stores temporary files in <filename>/tmp/</filename> by
default. When using a recovery disk with a small
<filename>/tmp</filename>, set <envar>TMPDIR</envar> to a
directory with more free space in order for the restore to
succeed.</para>
<para>When using <command>dump</command>, be aware that some
quirks remain from its early days in Version 6 of
AT&amp;T &unix;,circa 1975. The default parameters assume a
backup to a 9-track tape, rather than to another type of media
or to the high-density tapes available today. These defaults
must be overridden on the command line.</para>
<indexterm>
<primary><filename>.rhosts</filename></primary>
</indexterm>
<para>It is possible to backup a file system across the network
to a another system or to a tape drive attached to another
computer. While the &man.rdump.8; and &man.rrestore.8;
utilities can be used for this purpose, they are not
considered to be secure.</para>
<para>Instead, one can use <command>dump</command> and
<command>restore</command> in a more secure fashion over an
<acronym>SSH</acronym> connection. This example creates a
full, compressed backup of the <filename>/usr</filename> file
system and sends the backup file to the specified host over a
<acronym>SSH</acronym> connection.</para>
<example>
<title>Using <command>dump</command> over
<application>ssh</application></title>
<screen>&prompt.root; <userinput>/sbin/dump -0uan -f - /usr | gzip -2 | ssh -c blowfish \
targetuser@targetmachine.example.com dd of=/mybigfiles/dump-usr-l0.gz</userinput></screen>
</example>
<para>This example sets <envar>RSH</envar> in order to write the
backup to a tape drive on a remote system over a
<acronym>SSH</acronym> connection:</para>
<example>
<title>Using <command>dump</command> over
<application>ssh</application> with <envar>RSH</envar>
Set</title>
<screen>&prompt.root; <userinput>env RSH=/usr/bin/ssh /sbin/dump -0uan -f targetuser@targetmachine.example.com:/dev/sa0 /usr</userinput></screen>
</example>
</sect2>
<sect2>
<title>Directory Backups</title>
<indexterm>
<primary>backup software</primary>
<secondary><command>tar</command></secondary>
</indexterm>
<para>Several built-in utilities are available for backing up
and restoring specified files and directories as
needed.</para>
<para>A good choice for making a backup of all of the files in a
directory is &man.tar.1;. This utility dates back to Version
6 of AT&amp;T &unix; and by default assumes a recursive backup
to a local tape device. Switches can be used to instead
specify the name of a backup file.</para>
<indexterm><primary><command>tar</command></primary></indexterm>
<para>This example creates a compressed backup of the current
directory and saves it to
<filename>/tmp/mybackup.tgz</filename>. When creating a
backup file, make sure that the backup is not saved to the
same directory that is being backed up.</para>
<example>
<title>Backing Up the Current Directory With
<command>tar</command></title>
<screen>&prompt.root; <userinput>tar czvf <replaceable>/tmp/mybackup.tgz</replaceable> . </userinput></screen>
</example>
<para>To restore the entire backup, <command>cd</command> into
the directory to restore into and specify the name of the
backup. Note that this will overwrite any newer versions of
files in the restore directory. When in doubt, restore to a
temporary directory or specify the name of the file within the
backup to restore.</para>
<example>
<title>Restoring Up the Current Directory With
<command>tar</command></title>
<screen>&prompt.root; <userinput>tar xzvf <replaceable>/tmp/mybackup.tgz</replaceable></userinput></screen>
</example>
<para>There are dozens of available switches which are described
in &man.tar.1;. This utility also supports the use of exclude
patterns to specify which files should not be included when
backing up the specified directory or restoring files from a
backup.</para>
<indexterm>
<primary>backup software</primary>
<secondary><command>cpio</command></secondary>
</indexterm>
<para>To create a backup using a specified list of files and
directories, &man.cpio.1; is a good choice. Unlike
<command>tar</command>, <command>cpio</command> does not know
how to walk the directory tree and it must be provided the
list of files to backup.</para>
<para>For example, a list of files can be created using
<command>ls</command> or <command>find</command>. This
example creates a recursive listing of the current directory
which is then piped to <command>cpio</command> in order to
create an output backup file named
<filename>/tmp/mybackup.cpio</filename>.</para>
<example>
<title>Using<command>ls</command> and <command>cpio</command>
to Make a Recursive Backup of the Current Directory</title>
<screen>&prompt.root; <userinput>ls -R | cpio -ovF <replaceable>/tmp/mybackup.cpio</replaceable></userinput></screen>
</example>
<indexterm>
<primary>backup software</primary>
<secondary><command>pax</command></secondary>
</indexterm>
<indexterm><primary><command>pax</command></primary></indexterm>
<indexterm><primary>POSIX</primary></indexterm>
<indexterm><primary>IEEE</primary></indexterm>
<para>A backup utility which tries to bridge the features
provided by <command>tar</command> and <command>cpio</command>
is &man.pax.1;. Over the years, the various versions of
<command>tar</command> and <command>cpio</command> became
slightly incompatible. &posix; created <command>pax</command>
which attempts to read and write many of the various
<command>cpio</command> and <command>tar</command> formats,
plus new formats of its own.</para>
<para>The <command>pax</command> equivalent to the previous
examples would be:</para>
<example>
<title>Backing Up the Current Directory With
<command>pax</command></title>
<screen>&prompt.root; <userinput>pax -wf <replaceable>/tmp/mybackup.pax</replaceable> .</userinput></screen>
</example>
</sect2>
<sect2 xml:id="backups-tapebackups">
<title>Using Data Tapes for Backups</title>
<indexterm><primary>tape media</primary></indexterm>
<para>While tape technology has continued to evolve, modern
backup systems tend to combine off-site backups with local
removable media. &os; supports any tape drive that uses
<acronym>SCSI</acronym>, such as <acronym>LTO</acronym> or
<acronym>DAT</acronym>. There is limited support for
<acronym>SATA</acronym> and <acronym>USB</acronym> tape
drives.</para>
<para>For <acronym>SCSI</acronym> tape devices, &os; uses the
&man.sa.4; driver and the <filename>/dev/sa0</filename>,
<filename>/dev/nsa0</filename>, and
<filename>/dev/esa0</filename> devices. The physical device
name is <filename>/dev/sa0</filename>. When
<filename>/dev/nsa0</filename> is used, the backup application
will not rewind the tape after writing a file, which allows
writing more than one file to a tape. Using
<filename>/dev/esa0</filename> ejects the tape after the
device is closed.</para>
<para>In &os;, <command>mt</command> is used to control
operations of the tape drive, such as seeking through files on
a tape or writing tape control marks to the tape. For
example, the first three files on a tape can be preserved by
skipping past them before writing a new file:</para>
<screen>&prompt.root; <userinput>mt -f /dev/nsa0 fsf 3</userinput></screen>
<para>This utility supports many operations. Refer to
&man.mt.1; for details.</para>
<para>To write a single file to tape using
<command>tar</command>, specify the name of the tape device
and the file to backup:</para>
<screen>&prompt.root; <userinput>tar cvf /dev/sa0 <replaceable>file</replaceable></userinput></screen>
<para>To recover files from a <command>tar</command> archive
on tape into the current directory:</para>
<screen>&prompt.root; <userinput>tar xvf /dev/sa0</userinput></screen>
<para>To backup a <acronym>UFS</acronym> file system, use
<command>dump</command>. This examples backs up
<filename>/usr</filename> without rewinding the tape when
finished:</para>
<screen>&prompt.root; <userinput>dump -0aL -b64 -f /dev/nsa0 /usr</userinput></screen>
<para>To interactively restore files from a
<command>dump</command> file on tape into the current
directory:</para>
<screen>&prompt.root; <userinput>restore -i -f /dev/nsa0</userinput></screen>
</sect2>
<sect2 xml:id="backups-programs-amanda">
<title>Third-Party Backup Utilities</title>
<indexterm>
<primary>backup software</primary>
</indexterm>
<para>The &os; Ports Collection provides many third-party
utilities which can be used to schedule the creation of
backups, simplify tape backup, and make backups easier and
more convenient. Many of these applications are client/server
based and can be used to automate the backups of a single
system or all of the computers in a network.</para>
<para>Popular utilities include
<application>Amanda</application>,
<application>Bacula</application>,
<application>rsync</application>, and
<application>duplicity</application>.</para>
</sect2>
<sect2>
<title>Emergency Recovery</title>
<para>In addition to regular backups, it is recommended to
perform the following steps as part of an emergency
preparedness plan.</para>
<indexterm>
<primary><command>bsdlabel</command></primary></indexterm>
<para>Create a print copy of the output of the following
commands:</para>
<itemizedlist>
<listitem>
<para><command>gpart show</command></para>
</listitem>
<listitem>
<para><command>more /etc/fstab</command></para>
</listitem>
<listitem>
<para><command>dmesg</command></para>
</listitem>
</itemizedlist>
<indexterm><primary>livefs
<acronym>CD</acronym></primary></indexterm>
<para>Store this printout and a copy of the installation media
in a secure location. Should an emergency restore be
needed, boot into the installation media and select
<literal>Live CD</literal> to access a rescue shell. This
rescue mode can be used to view the current state of the
system, and if needed, to reformat disks and restore data
from backups.</para>
<note>
<para>The installation media for
&os;/&arch.i386;&nbsp;&rel2.current;-RELEASE does not
include a rescue shell. For this version, instead
download and burn a Livefs <acronym>CD</acronym> image from
<uri
xlink:href="ftp://ftp.FreeBSD.org/pub/FreeBSD/releases/&arch.i386;/ISO-IMAGES/&rel2.current;/&os;-&rel2.current;-RELEASE-&arch.i386;-livefs.iso">ftp://ftp.FreeBSD.org/pub/FreeBSD/releases/&arch.i386;/ISO-IMAGES/&rel2.current;/&os;-&rel2.current;-RELEASE-&arch.i386;-livefs.iso</uri>.</para>
</note>
<para>Next, test the rescue shell and the backups. Make notes
of the procedure. Store these notes with the media, the
printouts, and the backups. These notes may prevent the
inadvertent destruction of the backups while under the stress
of performing an emergency recovery.</para>
<para>For an added measure of security, store the latest backup
at a remote location which is physically separated from the
computers and disk drives by a significant distance.</para>
</sect2>
</sect1>
<sect1 xml:id="disks-virtual">
<info>
<title>Memory Disks</title>
<authorgroup>
<author>
<personname>
<firstname>Marc</firstname>
<surname>Fonvieille</surname>
</personname>
<contrib>Reorganized and enhanced by </contrib>
</author>
</authorgroup>
</info>
<para>In addition to physical disks, &os; also supports the
creation and use of memory disks. One possible use for a
memory disk is to access the contents of an
<acronym>ISO</acronym> file system without the overhead of first
burning it to a <acronym>CD</acronym> or <acronym>DVD</acronym>,
then mounting the <acronym>CD/DVD</acronym> media.</para>
<para>In &os;, the &man.md.4; driver is used to provide support
for memory disks. The <filename>GENERIC</filename> kernel
includes this driver. When using a custom kernel configuration
file, ensure it includes this line:</para>
<programlisting>device md</programlisting>
<sect2 xml:id="disks-mdconfig">
<title>Attaching and Detaching Existing Images</title>
<indexterm>
<primary>disks</primary>
<secondary>memory</secondary>
</indexterm>
<para>To mount an existing file system image, use
<command>mdconfig</command> to specify the name of the
<acronym>ISO</acronym> file and a free unit number. Then,
refer to that unit number to mount it on an existing mount
point. Once mounted, the files in the <acronym>ISO</acronym>
will appear in the mount point. This example attaches
<replaceable>diskimage.iso</replaceable> to the memory device
<filename>/dev/md0</filename> then mounts that memory device
on <filename>/mnt</filename>:</para>
<screen>&prompt.root; <userinput>mdconfig -f <replaceable>diskimage.iso</replaceable> -u <replaceable>0</replaceable></userinput>
&prompt.root; <userinput>mount /dev/md<replaceable>0</replaceable> <replaceable>/mnt</replaceable></userinput></screen>
<para>If a unit number is not specified with
<option>-u</option>, <command>mdconfig</command> will
automatically allocate an unused memory device and output
the name of the allocated unit, such as
<filename>md4</filename>. Refer to &man.mdconfig.8; for more
details about this command and its options.</para>
<indexterm>
<primary>disks</primary>
<secondary>detaching a memory disk</secondary>
</indexterm>
<para>When a memory disk is no longer in use, its resources
should be released back to the system. First, unmount the
file system, then use <command>mdconfig</command> to detach
the disk from the system and release its resources. To
continue this example:</para>
<screen>&prompt.root; <userinput>umount /mnt</userinput>
&prompt.root; <userinput>mdconfig -d -u <replaceable>0</replaceable></userinput></screen>
<para>To determine if any memory disks are still attached to the
system, type <command>mdconfig -l</command>.</para>
</sect2>
<sect2 xml:id="disks-md-freebsd5">
<title>Creating a File- or Memory-Backed Memory Disk</title>
<indexterm>
<primary>disks</primary>
<secondary>memory file system</secondary>
</indexterm>
<para>&os; also supports memory disks where the storage to use
is allocated from either a hard disk or an area of memory.
The first method is commonly referred to as a file-backed file
system and the second method as a memory-backed file system.
Both types can be created using
<command>mdconfig</command>.</para>
<para>To create a new memory-backed file system, specify a type
of <literal>swap</literal> and the size of the memory disk to
create. Then, format the memory disk with a file system and
mount as usual. This example creates a 5M memory disk on unit
<literal>1</literal>. That memory disk is then formatted with
the <acronym>UFS</acronym> file system before it is
mounted:</para>
<screen>&prompt.root; <userinput>mdconfig -a -t swap -s <replaceable>5</replaceable>m -u <replaceable>1</replaceable></userinput>
&prompt.root; <userinput>newfs -U md<replaceable>1</replaceable></userinput>
/dev/md1: 5.0MB (10240 sectors) block size 16384, fragment size 2048
using 4 cylinder groups of 1.27MB, 81 blks, 192 inodes.
with soft updates
super-block backups (for fsck -b #) at:
160, 2752, 5344, 7936
&prompt.root; <userinput>mount /dev/md<replaceable>1</replaceable> <replaceable>/mnt</replaceable></userinput>
&prompt.root; <userinput>df <replaceable>/mnt</replaceable></userinput>
Filesystem 1K-blocks Used Avail Capacity Mounted on
/dev/md1 4718 4 4338 0% /mnt</screen>
<para>To create a new file-backed memory disk, first allocate an
area of disk to use. This example creates an empty 5K file
named <filename>newimage</filename>:</para>
<screen>&prompt.root; <userinput>dd if=/dev/zero of=<replaceable>newimage</replaceable> bs=1k count=<replaceable>5</replaceable>k</userinput>
5120+0 records in
5120+0 records out</screen>
<para>Next, attach that file to a memory disk, label the memory
disk and format it with the <acronym>UFS</acronym> file
system, mount the memory disk, and verify the size of the
file-backed disk:</para>
<screen>&prompt.root; <userinput>mdconfig -f <replaceable>newimage</replaceable> -u <replaceable>0</replaceable></userinput>
&prompt.root; <userinput>bsdlabel -w md<replaceable>0</replaceable> auto</userinput>
&prompt.root; <userinput>newfs md<replaceable>0</replaceable>a</userinput>
/dev/md0a: 5.0MB (10224 sectors) block size 16384, fragment size 2048
using 4 cylinder groups of 1.25MB, 80 blks, 192 inodes.
super-block backups (for fsck -b #) at:
160, 2720, 5280, 7840
&prompt.root; <userinput>mount /dev/md<replaceable>0</replaceable>a <replaceable>/mnt</replaceable></userinput>
&prompt.root; <userinput>df <replaceable>/mnt</replaceable></userinput>
Filesystem 1K-blocks Used Avail Capacity Mounted on
/dev/md0a 4710 4 4330 0% /mnt</screen>
<para>It takes several commands to create a file- or
memory-backed file system using <command>mdconfig</command>.
&os; also comes with <command>mdmfs</command> which
automatically configures a memory disk, formats it with the
<acronym>UFS</acronym> file system, and mounts it. For
example, after creating <replaceable>newimage</replaceable>
with <command>dd</command>, this one command is equivalent to
running the <command>bsdlabel</command>,
<command>newfs</command>, and <command>mount</command>
commands shown above:</para>
<screen>&prompt.root; <userinput>mdmfs -F <replaceable>newimage</replaceable> -s <replaceable>5</replaceable>m md<replaceable>0</replaceable> <replaceable>/mnt</replaceable></userinput></screen>
<para>To instead create a new memory-based memory disk with
<command>mdmfs</command>, use this one command:</para>
<screen>&prompt.root; <userinput>mdmfs -s <replaceable>5</replaceable>m md<replaceable>1</replaceable> <replaceable>/mnt</replaceable></userinput></screen>
<para>If the unit number is not specified,
<command>mdmfs</command> will automatically select an unused
memory device. For more details about
<command>mdmfs</command>, refer to &man.mdmfs.8;.</para>
</sect2>
</sect1>
<sect1 xml:id="snapshots">
<info>
<title>File System Snapshots</title>
<authorgroup>
<author>
<personname>
<firstname>Tom</firstname>
<surname>Rhodes</surname>
</personname>
<contrib>Contributed by </contrib>
</author>
</authorgroup>
</info>
<indexterm>
<primary>file systems</primary>
<secondary>snapshots</secondary>
</indexterm>
<para>&os; offers a feature in conjunction with
<link linkend="soft-updates">Soft Updates</link>: file system
snapshots.</para>
<para>UFS snapshots allow a user to create images of specified
file systems, and treat them as a file. Snapshot files must be
created in the file system that the action is performed on, and
a user may create no more than 20 snapshots per file system.
Active snapshots are recorded in the superblock so they are
persistent across unmount and remount operations along with
system reboots. When a snapshot is no longer required, it can
be removed using &man.rm.1;. While snapshots may be removed in
any order, all the used space may not be acquired because
another snapshot will possibly claim some of the released
blocks.</para>
<para>The un-alterable <option>snapshot</option> file flag is set
by &man.mksnap.ffs.8; after initial creation of a snapshot file.
&man.unlink.1; makes an exception for snapshot files since it
allows them to be removed.</para>
<para>Snapshots are created using &man.mount.8;. To place a
snapshot of <filename>/var</filename> in the
file <filename>/var/snapshot/snap</filename>, use the following
command:</para>
<screen>&prompt.root; <userinput>mount -u -o snapshot /var/snapshot/snap /var</userinput></screen>
<para>Alternatively, use &man.mksnap.ffs.8; to create the
snapshot:</para>
<screen>&prompt.root; <userinput>mksnap_ffs /var /var/snapshot/snap</userinput></screen>
<para>One can find snapshot files on a file system, such as
<filename>/var</filename>, using
&man.find.1;:</para>
<screen>&prompt.root; <userinput>find /var -flags snapshot</userinput></screen>
<para>Once a snapshot has been created, it has several
uses:</para>
<itemizedlist>
<listitem>
<para>Some administrators will use a snapshot file for backup
purposes, because the snapshot can be transferred to
<acronym>CD</acronym>s or tape.</para>
</listitem>
<listitem>
<para>The file system integrity checker, &man.fsck.8;, may be
run on the snapshot. Assuming that the file system was
clean when it was mounted, this should always provide a
clean and unchanging result.</para>
</listitem>
<listitem>
<para>Running &man.dump.8; on the snapshot will produce a dump
file that is consistent with the file system and the
timestamp of the snapshot. &man.dump.8; can also take a
snapshot, create a dump image, and then remove the snapshot
in one command by using <option>-L</option>.</para>
</listitem>
<listitem>
<para>The snapshot can be mounted as a frozen image of the
file system. To &man.mount.8; the snapshot
<filename>/var/snapshot/snap</filename> run:</para>
<screen>&prompt.root; <userinput>mdconfig -a -t vnode -o readonly -f /var/snapshot/snap -u 4</userinput>
&prompt.root; <userinput>mount -r /dev/md4 /mnt</userinput></screen>
</listitem>
</itemizedlist>
<para>The frozen <filename>/var</filename> is now available
through <filename>/mnt</filename>. Everything will initially be
in the same state it was during the snapshot creation time. The
only exception is that any earlier snapshots will appear as zero
length files. To unmount the snapshot, use:</para>
<screen>&prompt.root; <userinput>umount /mnt</userinput>
&prompt.root; <userinput>mdconfig -d -u 4</userinput></screen>
<para>For more information about <option>softupdates</option> and
file system snapshots, including technical papers, visit
Marshall Kirk McKusick's website at <uri
xlink:href="http://www.mckusick.com/">http://www.mckusick.com/</uri>.</para>
</sect1>
<sect1 xml:id="quotas">
<title>Disk Quotas</title>
<indexterm>
<primary>accounting</primary>
<secondary>disk space</secondary>
</indexterm>
<indexterm><primary>disk quotas</primary></indexterm>
<para>Disk quotas can be used to limit the amount of disk space or
the number of files a user or members of a group may allocate on
a per-file system basis. This prevents one user or group of
users from consuming all of the available disk space.</para>
<para>This section describes how to configure disk quotas for the
<acronym>UFS</acronym> file system. To configure quotas on the
<acronym>ZFS</acronym> file system, refer to <xref
linkend="zfs-quotas"/></para>
<sect2>
<title>Enabling Disk Quotas</title>
<para>To determine if the &os; kernel provides support for disk
quotas:</para>
<screen>&prompt.user; <userinput>sysctl kern.features.ufs_quota</userinput>
kern.features.ufs_quota: 1</screen>
<para>In this example, the <literal>1</literal> indicates quota
support. If the value is instead <literal>0</literal>, add
the following line to a custom kernel configuration file and
rebuild the kernel using the instructions in <xref
linkend="kernelconfig"/>:</para>
<programlisting>options QUOTA</programlisting>
<para>Next, enable disk quotas in
<filename>/etc/rc.conf</filename>:</para>
<programlisting>quota_enable="YES"</programlisting>
<indexterm>
<primary>disk quotas</primary>
<secondary>checking</secondary>
</indexterm>
<para>Normally on bootup, the quota integrity of each file
system is checked by &man.quotacheck.8;. This program insures
that the data in the quota database properly reflects the data
on the file system. This is a time consuming process that
will significantly affect the time the system takes to boot.
To skip this step, add this variable to
<filename>/etc/rc.conf</filename>:</para>
<programlisting>check_quotas="NO"</programlisting>
<para>Finally, edit <filename>/etc/fstab</filename> to enable
disk quotas on a per-file system basis. To enable per-user
quotas on a file system, add <option>userquota</option> to the
options field in the <filename>/etc/fstab</filename> entry for
the file system to enable quotas on. For example:</para>
<programlisting>/dev/da1s2g /home ufs rw,userquota 1 2</programlisting>
<para>To enable group quotas, use <option>groupquota</option>
instead. To enable both user and group quotas, separate the
options with a comma:</para>
<programlisting>/dev/da1s2g /home ufs rw,userquota,groupquota 1 2</programlisting>
<para>By default, quota files are stored in the root directory
of the file system as <filename>quota.user</filename> and
<filename>quota.group</filename>. Refer to &man.fstab.5; for
more information. Specifying an alternate location for the
quota files is not recommended.</para>
<para>Once the configuration is complete, reboot the system and
<filename>/etc/rc</filename> will automatically run the
appropriate commands to create the initial quota files for all
of the quotas enabled in
<filename>/etc/fstab</filename>.</para>
<para>In the normal course of operations, there should be no
need to manually run &man.quotacheck.8;, &man.quotaon.8;, or
&man.quotaoff.8;. However, one should read these manual pages
to be familiar with their operation.</para>
</sect2>
<sect2>
<title>Setting Quota Limits</title>
<indexterm>
<primary>disk quotas</primary>
<secondary>limits</secondary>
</indexterm>
<para>To
verify that quotas are enabled, run:</para>
<screen>&prompt.root; <userinput>quota -v</userinput></screen>
<para>There should be a one line summary of disk usage and
current quota limits for each file system that quotas are
enabled on.</para>
<para>The system is now ready to be assigned quota limits with
<command>edquota</command>.</para>
<para>Several options are available to enforce limits on the
amount of disk space a user or group may allocate, and how
many files they may create. Allocations can be limited based
on disk space (block quotas), number of files (inode quotas),
or a combination of both. Each limit is further broken down
into two categories: hard and soft limits.</para>
<indexterm><primary>hard limit</primary></indexterm>
<para>A hard limit may not be exceeded. Once a user reaches a
hard limit, no further allocations can be made on that file
system by that user. For example, if the user has a hard
limit of 500 kbytes on a file system and is currently using
490 kbytes, the user can only allocate an additional 10
kbytes. Attempting to allocate an additional 11 kbytes will
fail.</para>
<indexterm><primary>soft limit</primary></indexterm>
<para>Soft limits can be exceeded for a limited amount of time,
known as the grace period, which is one week by default. If a
user stays over their limit longer than the grace period, the
soft limit turns into a hard limit and no further allocations
are allowed. When the user drops back below the soft limit,
the grace period is reset.</para>
<para>In the following example, the quota for the <systemitem
class="username">test</systemitem> account is being edited.
When <command>edquota</command> is invoked, the editor
specified by <envar>EDITOR</envar> is opened in order to edit
the quota limits. The default editor is set to
<application>vi</application>.</para>
<screen>&prompt.root; <userinput>edquota -u test</userinput>
Quotas for user test:
/usr: kbytes in use: 65, limits (soft = 50, hard = 75)
inodes in use: 7, limits (soft = 50, hard = 60)
/usr/var: kbytes in use: 0, limits (soft = 50, hard = 75)
inodes in use: 0, limits (soft = 50, hard = 60)</screen>
<para>There are normally two lines for each file system that has
quotas enabled. One line represents the block limits and the
other represents the inode limits. Change the value to modify
the quota limit. For example, to raise the block limit on
<filename>/usr</filename> to a soft limit of
<literal>500</literal> and a hard limit of
<literal>600</literal>, change the values in that line as
follows:</para>
<programlisting>/usr: kbytes in use: 65, limits (soft = 500, hard = 600)</programlisting>
<para>The new quota limits take affect upon exiting the
editor.</para>
<para>Sometimes it is desirable to set quota limits on a range
of users. This can be done by first assigning the desired
quota limit to a user. Then, use <option>-p</option> to
duplicate that quota to a specified range of user IDs
(<acronym>UID</acronym>s). The following command will
duplicate those quota limits for <acronym>UID</acronym>s
<literal>10,000</literal> through
<literal>19,999</literal>:</para>
<screen>&prompt.root; <userinput>edquota -p test 10000-19999</userinput></screen>
<para>For more information, refer to &man.edquota.8;.</para>
</sect2>
<sect2>
<title>Checking Quota Limits and Disk Usage</title>
<indexterm>
<primary>disk quotas</primary>
<secondary>checking</secondary>
</indexterm>
<para>To check individual user or group quotas and disk usage,
use &man.quota.1;. A user may only examine their own quota
and the quota of a group they are a member of. Only the
superuser may view all user and group quotas. To get a
summary of all quotas and disk usage for file systems with
quotas enabled, use &man.repquota.8;.</para>
<para>Normally, file systems that the user is not using any disk
space on will not show in the output of
<command>quota</command>, even if the user has a quota limit
assigned for that file system. Use <option>-v</option> to
display those file systems. The following is sample output
from <command>quota -v</command> for a user that has quota
limits on two file systems.</para>
<programlisting>Disk quotas for user test (uid 1002):
Filesystem usage quota limit grace files quota limit grace
/usr 65* 50 75 5days 7 50 60
/usr/var 0 50 75 0 50 60</programlisting>
<indexterm><primary>grace period</primary></indexterm>
<para>In this example, the user is currently 15 kbytes over the
soft limit of 50 kbytes on <filename>/usr</filename> and has 5
days of grace period left. The asterisk <literal>*</literal>
indicates that the user is currently over the quota
limit.</para>
</sect2>
<sect2>
<title>Quotas over NFS</title>
<indexterm><primary>NFS</primary></indexterm>
<para>Quotas are enforced by the quota subsystem on the
<acronym>NFS</acronym> server. The &man.rpc.rquotad.8; daemon
makes quota information available to <command>quota</command>
on <acronym>NFS</acronym> clients, allowing users on those
machines to see their quota statistics.</para>
<para>On the <acronym>NFS</acronym> server, enable
<command>rpc.rquotad</command> by removing the
<literal>#</literal> from this line in
<filename>/etc/inetd.conf</filename>:</para>
<programlisting>rquotad/1 dgram rpc/udp wait root /usr/libexec/rpc.rquotad rpc.rquotad</programlisting>
<para>Then, restart <command>inetd</command>:</para>
<screen>&prompt.root; <userinput>service inetd restart</userinput></screen>
</sect2>
</sect1>
<sect1 xml:id="disks-encrypting">
<info>
<title>Encrypting Disk Partitions</title>
<authorgroup>
<author>
<personname>
<firstname>Lucky</firstname>
<surname>Green</surname>
</personname>
<contrib>Contributed by </contrib>
<affiliation>
<address>
<email>shamrock@cypherpunks.to</email>
</address>
</affiliation>
</author>
</authorgroup>
</info>
<indexterm>
<primary>disks</primary>
<secondary>encrypting</secondary>
</indexterm>
<para>&os; offers excellent online protections against
unauthorized data access. File permissions and <link
linkend="mac">Mandatory Access Control</link> (MAC) help
prevent unauthorized users from accessing data while the
operating system is active and the computer is powered up.
However, the permissions enforced by the operating system are
irrelevant if an attacker has physical access to a computer and
can move the computer's hard drive to another system to copy and
analyze the data.</para>
<para>Regardless of how an attacker may have come into possession
of a hard drive or powered-down computer, the
<acronym>GEOM</acronym>-based cryptographic subsystems built
into &os; are able to protect the data on the computer's file
systems against even highly-motivated attackers with significant
resources. Unlike encryption methods that encrypt individual
files, the built-in <command>gbde</command> and
<command>geli</command> utilities can be used to transparently
encrypt entire file systems. No cleartext ever touches the hard
drive's platter.</para>
<para>This chapter demonstrates how to create an encrypted file
system on &os;. It first demonstrates the process using
<command>gbde</command> and then demonstrates the same example
using <command>geli</command>.</para>
<sect2>
<title>Disk Encryption with
<application>gbde</application></title>
<para>The objective of the &man.gbde.4; facility is to provide a
formidable challenge for an attacker to gain access to the
contents of a <emphasis>cold</emphasis> storage device.
However, if the computer is compromised while up and running
and the storage device is actively attached, or the attacker
has access to a valid passphrase, it offers no protection to
the contents of the storage device. Thus, it is important to
provide physical security while the system is running and to
protect the passphrase used by the encryption
mechanism.</para>
<para>This facility provides several barriers to protect the
data stored in each disk sector. It encrypts the contents of
a disk sector using 128-bit <acronym>AES</acronym> in
<acronym>CBC</acronym> mode. Each sector on the disk is
encrypted with a different <acronym>AES</acronym> key. For
more information on the cryptographic design, including how
the sector keys are derived from the user-supplied passphrase,
refer to &man.gbde.4;.</para>
<para>&os; provides a kernel module for
<application>gbde</application> which can be loaded with this
command:</para>
<screen>&prompt.root; <userinput>kldload geom_bde</userinput></screen>
<para>If using a custom kernel configuration file, ensure it
contains this line:</para>
<para><literal>options GEOM_BDE</literal></para>
<para>The following example demonstrates adding a new hard drive
to a system that will hold a single encrypted partition that
will be mounted as <filename>/private</filename>.</para>
<procedure>
<title>Encrypting a Partition with
<application>gbde</application></title>
<step>
<title>Add the New Hard Drive</title>
<para>Install the new drive to the system as explained in
<xref linkend="disks-adding"/>. For the purposes of this
example, a new hard drive partition has been added as
<filename>/dev/ad4s1c</filename> and
<filename>/dev/ad0s1<replaceable>*</replaceable></filename>
represents the existing standard &os; partitions.</para>
<screen>&prompt.root; <userinput>ls /dev/ad*</userinput>
/dev/ad0 /dev/ad0s1b /dev/ad0s1e /dev/ad4s1
/dev/ad0s1 /dev/ad0s1c /dev/ad0s1f /dev/ad4s1c
/dev/ad0s1a /dev/ad0s1d /dev/ad4</screen>
</step>
<step>
<title>Create a Directory to Hold <command>gbde</command>
Lock Files</title>
<screen>&prompt.root; <userinput>mkdir /etc/gbde</userinput></screen>
<para>The <application>gbde</application> lock file
contains information that <application>gbde</application>
requires to access encrypted partitions. Without access
to the lock file, <application>gbde</application> will not
be able to decrypt the data contained in the encrypted
partition without significant manual intervention which is
not supported by the software. Each encrypted partition
uses a separate lock file.</para>
</step>
<step>
<title>Initialize the <command>gbde</command>
Partition</title>
<para>A <application>gbde</application> partition must be
initialized before it can be used. This initialization
needs to be performed only once. This command will open
the default editor, in order to set various configuration
options in a template. For use with the
<acronym>UFS</acronym> file system, set the sector_size to
2048:</para>
<screen>&prompt.root; <userinput>gbde init /dev/ad4s1c -i -L /etc/gbde/ad4s1c.lock</userinput># &dollar;FreeBSD: src/sbin/gbde/template.txt,v 1.1.36.1 2009/08/03 08:13:06 kensmith Exp $
#
# Sector size is the smallest unit of data which can be read or written.
# Making it too small decreases performance and decreases available space.
# Making it too large may prevent filesystems from working. 512 is the
# minimum and always safe. For UFS, use the fragment size
#
sector_size = 2048
[...]</screen>
<para>Once the edit is saved, the user will be asked twice
to type the passphrase used to secure the data. The
passphrase must be the same both times. The ability of
<application>gbde</application> to protect data depends
entirely on the quality of the passphrase. For tips on
how to select a secure passphrase that is easy to
remember, see <link
xlink:href="http://world.std.com/~reinhold/diceware.html">http://world.std.com/~reinhold/diceware.htm</link>.</para>
<para>This initialization creates a lock file for the
<application>gbde</application> partition. In this
example, it is stored as
<filename>/etc/gbde/ad4s1c.lock</filename>. Lock files
must end in <quote>.lock</quote> in order to be correctly
detected by the <filename>/etc/rc.d/gbde</filename> start
up script.</para>
<caution>
<para>Lock files <emphasis>must</emphasis> be backed up
together with the contents of any encrypted partitions.
Without the lock file, the legitimate owner will be
unable to access the data on the encrypted
partition.</para>
</caution>
</step>
<step>
<title>Attach the Encrypted Partition to the
Kernel</title>
<screen>&prompt.root; <userinput>gbde attach /dev/ad4s1c -l /etc/gbde/ad4s1c.lock</userinput></screen>
<para>This command will prompt to input the passphrase that
was selected during the initialization of the encrypted
partition. The new encrypted device will appear in
<filename>/dev</filename> as
<filename>/dev/device_name.bde</filename>:</para>
<screen>&prompt.root; <userinput>ls /dev/ad*</userinput>
/dev/ad0 /dev/ad0s1b /dev/ad0s1e /dev/ad4s1
/dev/ad0s1 /dev/ad0s1c /dev/ad0s1f /dev/ad4s1c
/dev/ad0s1a /dev/ad0s1d /dev/ad4 /dev/ad4s1c.bde</screen>
</step>
<step>
<title>Create a File System on the Encrypted
Device</title>
<para>Once the encrypted device has been attached to the
kernel, a file system can be created on the device. This
example creates a <acronym>UFS</acronym> file system with
soft updates enabled. Be sure to specify the partition
which has a
<filename><replaceable>*</replaceable>.bde</filename>
extension:</para>
<screen>&prompt.root; <userinput>newfs -U /dev/ad4s1c.bde</userinput></screen>
</step>
<step>
<title>Mount the Encrypted Partition</title>
<para>Create a mount point and mount the encrypted file
system:</para>
<screen>&prompt.root; <userinput>mkdir /private</userinput>
&prompt.root; <userinput>mount /dev/ad4s1c.bde /private</userinput></screen>
</step>
<step>
<title>Verify That the Encrypted File System is
Available</title>
<para>The encrypted file system should now be visible and
available for use:</para>
<screen>&prompt.user; <userinput>df -H</userinput>
Filesystem Size Used Avail Capacity Mounted on
/dev/ad0s1a 1037M 72M 883M 8% /
/devfs 1.0K 1.0K 0B 100% /dev
/dev/ad0s1f 8.1G 55K 7.5G 0% /home
/dev/ad0s1e 1037M 1.1M 953M 0% /tmp
/dev/ad0s1d 6.1G 1.9G 3.7G 35% /usr
/dev/ad4s1c.bde 150G 4.1K 138G 0% /private</screen>
</step>
</procedure>
<para>After each boot, any encrypted file systems must be
manually re-attached to the kernel, checked for errors, and
mounted, before the file systems can be used. To configure
these steps, add the following lines to
<filename>/etc/rc.conf</filename>:</para>
<programlisting>gbde_autoattach_all="YES"
gbde_devices="<replaceable>ad4s1c</replaceable>"
gbde_lockdir="/etc/gbde"</programlisting>
<para>This requires that the passphrase be entered at the
console at boot time. After typing the correct passphrase,
the encrypted partition will be mounted automatically.
Additional <application>gbde</application> boot options are
available and listed in &man.rc.conf.5;.</para>
<!--
What about bsdinstall?
-->
<note>
<para><application>sysinstall</application> is incompatible
with <application>gbde</application>-encrypted devices. All
<filename>*.bde</filename> devices must be detached from the
kernel before starting <application>sysinstall</application>
or it will crash during its initial probing for devices. To
detach the encrypted device used in the example, use the
following command:</para>
<screen>&prompt.root; <userinput>gbde detach /dev/<replaceable>ad4s1c</replaceable></userinput></screen>
</note>
</sect2>
<sect2 xml:id="disks-encrypting-geli">
<info>
<title>Disk Encryption with <command>geli</command></title>
<authorgroup>
<author>
<personname>
<firstname>Daniel</firstname>
<surname>Gerzo</surname>
</personname>
<contrib>Contributed by </contrib>
</author>
</authorgroup>
</info>
<para>An alternative cryptographic <acronym>GEOM</acronym> class
is available using <command>geli</command>. This control
utility adds some features and uses a different scheme for
doing cryptographic work. It provides the following
features:</para>
<itemizedlist>
<listitem>
<para>Utilizes the &man.crypto.9; framework and
automatically uses cryptographic hardware when it is
available.</para>
</listitem>
<listitem>
<para>Supports multiple cryptographic algorithms such as
<acronym>AES</acronym>, Blowfish, and
<acronym>3DES</acronym>.</para>
</listitem>
<listitem>
<para>Allows the root partition to be encrypted. The
passphrase used to access the encrypted root partition
will be requested during system boot.</para>
</listitem>
<listitem>
<para>Allows the use of two independent keys.</para>
</listitem>
<listitem>
<para>It is fast as it performs simple sector-to-sector
encryption.</para>
</listitem>
<listitem>
<para>Allows backup and restore of master keys. If a user
destroys their keys, it is still possible to get access to
the data by restoring keys from the backup.</para>
</listitem>
<listitem>
<para>Allows a disk to attach with a random, one-time key
which is useful for swap partitions and temporary file
systems.</para>
</listitem>
</itemizedlist>
<para>More features and usage examples can be found in
&man.geli.8;.</para>
<para>The following example describes how to generate a key file
which will be used as part of the master key for the encrypted
provider mounted under <filename>/private</filename>. The key
file will provide some random data used to encrypt the master
key. The master key will also be protected by a passphrase.
The provider's sector size will be 4kB. The example describes
how to attach to the <command>geli</command> provider, create
a file system on it, mount it, work with it, and finally, how
to detach it.</para>
<procedure>
<title>Encrypting a Partition with
<command>geli</command></title>
<step>
<title>Load <command>geli</command> Support</title>
<para>Support for <command>geli</command> is built into the
<filename>GENERIC</filename> kernel. To configure the
system to automatically load the module
at boot time, add the following line to
<filename>/boot/loader.conf</filename>:</para>
<programlisting>geom_eli_load="YES"</programlisting>
<para>To load the kernel module now:</para>
<screen>&prompt.root; <userinput>kldload geom_eli</userinput></screen>
<para>For a custom kernel, ensure the kernel configuration
file contains these lines:</para>
<programlisting>options GEOM_ELI
device crypto</programlisting>
</step>
<step>
<title>Generate the Master Key</title>
<para>The following commands generate a master key
(<filename>/root/da2.key</filename>) that is protected
with a passphrase. The data source for the key file is
<filename>/dev/random</filename> and the sector size of
the provider (<filename>/dev/da2.eli</filename>) is 4kB as
a bigger sector size provides better performance:</para>
<screen>&prompt.root; <userinput>dd if=/dev/random of=/root/da2.key bs=64 count=1</userinput>
&prompt.root; <userinput>geli init -s 4096 -K /root/da2.key /dev/da2</userinput>
Enter new passphrase:
Reenter new passphrase:</screen>
<para>It is not mandatory to use both a passphrase and a key
file as either method of securing the master key can be
used in isolation.</para>
<para>If the key file is given as <quote>-</quote>, standard
input will be used. For example, this command generates
three key files:</para>
<screen>&prompt.root; <userinput>cat keyfile1 keyfile2 keyfile3 | geli init -K - /dev/da2</userinput></screen>
</step>
<step>
<title>Attach the Provider with the Generated Key</title>
<para>To attach the provider, specify the key file, the name
of the disk, and the passphrase:</para>
<screen>&prompt.root; <userinput>geli attach -k /root/da2.key /dev/da2</userinput>
Enter passphrase:</screen>
<para>This creates a new device with an
<filename>.eli</filename> extension:</para>
<screen>&prompt.root; <userinput>ls /dev/da2*</userinput>
/dev/da2 /dev/da2.eli</screen>
</step>
<step>
<title>Create the New File System</title>
<para>Next, format the device with the
<acronym>UFS</acronym> file system and mount it on an
existing mount point:</para>
<screen>&prompt.root; <userinput>dd if=/dev/random of=/dev/da2.eli bs=1m</userinput>
&prompt.root; <userinput>newfs /dev/da2.eli</userinput>
&prompt.root; <userinput>mount /dev/da2.eli <replaceable>/private</replaceable></userinput></screen>
<para>The encrypted file system should now be available for
use:</para>
<screen>&prompt.root; <userinput>df -H</userinput>
Filesystem Size Used Avail Capacity Mounted on
/dev/ad0s1a 248M 89M 139M 38% /
/devfs 1.0K 1.0K 0B 100% /dev
/dev/ad0s1f 7.7G 2.3G 4.9G 32% /usr
/dev/ad0s1d 989M 1.5M 909M 0% /tmp
/dev/ad0s1e 3.9G 1.3G 2.3G 35% /var
/dev/da2.eli 150G 4.1K 138G 0% /private</screen>
</step>
</procedure>
<para>Once the work on the encrypted partition is done, and the
<filename>/private</filename> partition is no longer needed,
it is prudent to put the device into cold storage by
unmounting and detaching the <command>geli</command> encrypted
partition from the kernel:</para>
<screen>&prompt.root; <userinput>umount /private</userinput>
&prompt.root; <userinput>geli detach da2.eli</userinput></screen>
<para>A <filename>rc.d</filename> script is provided to
simplify the mounting of <command>geli</command>-encrypted
devices at boot time. For this example, add these lines to
<filename>/etc/rc.conf</filename>:</para>
<programlisting>geli_devices="<replaceable>da2</replaceable>"
geli_da2_flags="-p -k /root/<replaceable>da2.key</replaceable>"</programlisting>
<para>This configures <filename>/dev/da2</filename> as a
<command>geli</command> provider with a master key of
<filename>/root/da2.key</filename>. The system will
automatically detach the provider from the kernel before the
system shuts down. During the startup process, the script
will prompt for the passphrase before attaching the provider.
Other kernel messages might be shown before and after the
password prompt. If the boot process seems to stall, look
carefully for the password prompt among the other messages.
Once the correct passphrase is entered, the provider is
attached. The file system is then mounted, typically by an
entry in <filename>/etc/fstab</filename>. Refer to <xref
linkend="mount-unmount"/> for instructions on how to
configure a file system to mount at boot time.</para>
</sect2>
</sect1>
<sect1 xml:id="swap-encrypting">
<info>
<title>Encrypting Swap</title>
<authorgroup>
<author>
<personname>
<firstname>Christian</firstname>
<surname>Br&uuml;ffer</surname>
</personname>
<contrib>Written by </contrib>
</author>
</authorgroup>
</info>
<indexterm>
<primary>swap</primary>
<secondary>encrypting</secondary>
</indexterm>
<para>Like the encryption of disk partitions, encryption of swap
space is used to protect sensitive information. Consider an
application that deals with passwords. As long as these
passwords stay in physical memory, they are not written to disk
and will be cleared after a reboot. However, if &os; starts
swapping out memory pages to free space, the passwords may be
written to the disk unencrypted. Encrypting swap space can be a
solution for this scenario.</para>
<para>This section demonstrates how to configure an encrypted
swap partition using &man.gbde.8; or &man.geli.8; encryption.
It assumes a <acronym>UFS</acronym> file system where
<filename>/dev/ad0s1b</filename> is the swap partition.</para>
<sect2>
<title>Configuring Encrypted Swap</title>
<para>Swap partitions are not encrypted by default and should be
cleared of any sensitive data before continuing. To overwrite
the current swap partition with random garbage, execute the
following command:</para>
<screen>&prompt.root; <userinput>dd if=/dev/random of=/dev/<replaceable>ad0s1b</replaceable> bs=1m</userinput></screen>
<para>To encrypt the swap partition using &man.gbde.8;, add the
<literal>.bde</literal> suffix to the swap line in
<filename>/etc/fstab</filename>:</para>
<programlisting># Device Mountpoint FStype Options Dump Pass#
/dev/ad0s1b.bde none swap sw 0 0</programlisting>
<para>To instead encrypt the swap partition using &man.geli.8;,
use the
<literal>.eli</literal> suffix:</para>
<programlisting># Device Mountpoint FStype Options Dump Pass#
/dev/ad0s1b.eli none swap sw 0 0</programlisting>
<para>By default, &man.geli.8; uses the <acronym>AES</acronym>
algorithm with a key length of 128 bit. These defaults can be
altered by using <literal>geli_swap_flags</literal> in
<filename>/etc/rc.conf</filename>. The following flags
configure encryption using the Blowfish algorithm with a key
length of 128 bits and a sectorsize of 4 kilobytes, and sets
<quote>detach on last close</quote>:</para>
<programlisting>geli_swap_flags="-e blowfish -l 128 -s 4096 -d"</programlisting>
<para>Refer to the description of <literal>onetime</literal> in
&man.geli.8; for a list of possible options.</para>
</sect2>
<sect2>
<title>Encrypted Swap Verification</title>
<para>Once the system has rebooted, proper operation of the
encrypted swap can be verified using
<command>swapinfo</command>.</para>
<para>If &man.gbde.8; is being used:</para>
<screen>&prompt.user; <userinput>swapinfo</userinput>
Device 1K-blocks Used Avail Capacity
/dev/ad0s1b.bde 542720 0 542720 0%</screen>
<para>If &man.geli.8; is being used:</para>
<screen>&prompt.user; <userinput>swapinfo</userinput>
Device 1K-blocks Used Avail Capacity
/dev/ad0s1b.eli 542720 0 542720 0%</screen>
</sect2>
</sect1>
<sect1 xml:id="disks-hast">
<info>
<title>Highly Available Storage
(<acronym>HAST</acronym>)</title>
<authorgroup>
<author>
<personname>
<firstname>Daniel</firstname>
<surname>Gerzo</surname>
</personname>
<contrib>Contributed by </contrib>
</author>
</authorgroup>
<authorgroup>
<author>
<personname>
<firstname>Freddie</firstname>
<surname>Cash</surname>
</personname>
<contrib>With inputs from </contrib>
</author>
<author>
<personname>
<firstname>Pawel Jakub</firstname>
<surname>Dawidek</surname>
</personname>
</author>
<author>
<personname>
<firstname>Michael W.</firstname>
<surname>Lucas</surname>
</personname>
</author>
<author>
<personname>
<firstname>Viktor</firstname>
<surname>Petersson</surname>
</personname>
</author>
</authorgroup>
</info>
<indexterm>
<primary>HAST</primary>
<secondary>high availability</secondary>
</indexterm>
<para>High availability is one of the main requirements in
serious business applications and highly-available storage is a
key component in such environments. In &os;, the Highly
Available STorage (<acronym>HAST</acronym>) framework allows
transparent storage of the same data across several physically
separated machines connected by a <acronym>TCP/IP</acronym>
network. <acronym>HAST</acronym> can be understood as a
network-based RAID1 (mirror), and is similar to the DRBD&reg;
storage system used in the GNU/&linux; platform. In combination
with other high-availability features of &os; like
<acronym>CARP</acronym>, <acronym>HAST</acronym> makes it
possible to build a highly-available storage cluster that is
resistant to hardware failures.</para>
<para>The following are the main features of
<acronym>HAST</acronym>:</para>
<itemizedlist>
<listitem>
<para>Can be used to mask <acronym>I/O</acronym> errors on
local hard drives.</para>
</listitem>
<listitem>
<para>File system agnostic as it works with any file system
supported by &os;.</para>
</listitem>
<listitem>
<para>Efficient and quick resynchronization as only the blocks
that were modified during the downtime of a node are
synchronized.</para>
</listitem>
<!--
<listitem>
<para>Has several synchronization modes to allow for fast
failover.</para>
</listitem>
-->
<listitem>
<para>Can be used in an already deployed environment to add
additional redundancy.</para>
</listitem>
<listitem>
<para>Together with <acronym>CARP</acronym>,
<application>Heartbeat</application>, or other tools, it can
be used to build a robust and durable storage system.</para>
</listitem>
</itemizedlist>
<para>After reading this section, you will know:</para>
<itemizedlist>
<listitem>
<para>What <acronym>HAST</acronym> is, how it works, and
which features it provides.</para>
</listitem>
<listitem>
<para>How to set up and use <acronym>HAST</acronym> on
&os;.</para>
</listitem>
<listitem>
<para>How to integrate <acronym>CARP</acronym> and
&man.devd.8; to build a robust storage system.</para>
</listitem>
</itemizedlist>
<para>Before reading this section, you should:</para>
<itemizedlist>
<listitem>
<para>Understand &unix; and &os; basics (<xref
linkend="basics"/>).</para>
</listitem>
<listitem>
<para>Know how to configure network
interfaces and other core &os; subsystems (<xref
linkend="config-tuning"/>).</para>
</listitem>
<listitem>
<para>Have a good understanding of &os;
networking (<xref
linkend="network-communication"/>).</para>
</listitem>
</itemizedlist>
<para>The <acronym>HAST</acronym> project was sponsored by The
&os; Foundation with support from <link
xlink:href="http://www.omc.net/">http://www.omc.net/</link>
and <link
xlink:href="http://www.transip.nl/">http://www.transip.nl/</link>.</para>
<sect2>
<title>HAST Operation</title>
<para><acronym>HAST</acronym> provides synchronous block-level
replication between two physical machines: the
<emphasis>primary</emphasis>, also known as the
<emphasis>master</emphasis> node, and the
<emphasis>secondary</emphasis>, or <emphasis>slave</emphasis>
node. These two machines together are referred to as a
cluster.</para>
<para>Since <acronym>HAST</acronym> works in a primary-secondary
configuration, it allows only one of the cluster nodes to be
active at any given time. The primary node, also called
<emphasis>active</emphasis>, is the one which will handle all
the <acronym>I/O</acronym> requests to
<acronym>HAST</acronym>-managed devices. The secondary node
is automatically synchronized from the primary node.</para>
<para>The physical components of the <acronym>HAST</acronym>
system are the local disk on primary node, and the disk on the
remote, secondary node.</para>
<para><acronym>HAST</acronym> operates synchronously on a block
level, making it transparent to file systems and applications.
<acronym>HAST</acronym> provides regular GEOM providers in
<filename>/dev/hast/</filename> for use by other tools or
applications. There is no difference between using
<acronym>HAST</acronym>-provided devices and raw disks or
partitions.</para>
<para>Each write, delete, or flush operation is sent to both the
local disk and to the remote disk over
<acronym>TCP/IP</acronym>. Each read operation is served from
the local disk, unless the local disk is not up-to-date or an
<acronym>I/O</acronym> error occurs. In such cases, the read
operation is sent to the secondary node.</para>
<para><acronym>HAST</acronym> tries to provide fast failure
recovery. For this reason, it is important to reduce
synchronization time after a node's outage. To provide fast
synchronization, <acronym>HAST</acronym> manages an on-disk
bitmap of dirty extents and only synchronizes those during a
regular synchronization, with an exception of the initial
sync.</para>
<para>There are many ways to handle synchronization.
<acronym>HAST</acronym> implements several replication modes
to handle different synchronization methods:</para>
<itemizedlist>
<listitem>
<para><emphasis>memsync</emphasis>: This mode reports a
write operation as completed when the local write
operation is finished and when the remote node
acknowledges data arrival, but before actually storing the
data. The data on the remote node will be stored directly
after sending the acknowledgement. This mode is intended
to reduce latency, but still provides good
reliability.</para>
</listitem>
<listitem>
<para><emphasis>fullsync</emphasis>: This mode reports a
write operation as completed when both the local write and
the remote write complete. This is the safest and the
slowest replication mode. This mode is the
default.</para>
</listitem>
<listitem>
<para><emphasis>async</emphasis>: This mode reports a write
operation as completed when the local write completes.
This is the fastest and the most dangerous replication
mode. It should only be used when replicating to a
distant node where latency is too high for other
modes.</para>
</listitem>
</itemizedlist>
</sect2>
<sect2>
<title>HAST Configuration</title>
<para>The <acronym>HAST</acronym> framework consists of several
components:</para>
<itemizedlist>
<listitem>
<para>The &man.hastd.8; daemon which provides data
synchronization. When this daemon is started, it will
automatically load <varname>geom_gate.ko</varname>.</para>
</listitem>
<listitem>
<para>The userland management utility,
&man.hastctl.8;.</para>
</listitem>
<listitem>
<para>The &man.hast.conf.5; configuration file. This file
must exist before starting
<application>hastd</application>.</para>
</listitem>
</itemizedlist>
<para>Users who prefer to statically build
<literal>GEOM_GATE</literal> support into the kernel should
add this line to the custom kernel configuration file, then
rebuild the kernel using the instructions in <xref
linkend="kernelconfig"/>:</para>
<programlisting>options GEOM_GATE</programlisting>
<para>The following example describes how to configure two nodes
in master-slave/primary-secondary operation using
<acronym>HAST</acronym> to replicate the data between the two.
The nodes will be called <literal>hasta</literal>, with an
<acronym>IP</acronym> address of
<literal>172.16.0.1</literal>, and <literal>hastb</literal>,
with an <acronym>IP</acronym> address of
<literal>172.16.0.2</literal>. Both nodes will have a
dedicated hard drive <filename>/dev/ad6</filename> of the same
size for <acronym>HAST</acronym> operation. The
<acronym>HAST</acronym> pool, sometimes referred to as a
resource or the <acronym>GEOM</acronym> provider in <filename
class="directory">/dev/hast/</filename>, will be called
<literal>test</literal>.</para>
<para>Configuration of <acronym>HAST</acronym> is done using
<filename>/etc/hast.conf</filename>. This file should be
identical on both nodes. The simplest configuration
is:</para>
<programlisting>resource <replaceable>test</replaceable> {
on <replaceable>hasta</replaceable> {
local <replaceable>/dev/ad6</replaceable>
remote <replaceable>172.16.0.2</replaceable>
}
on <replaceable>hastb</replaceable> {
local <replaceable>/dev/ad6</replaceable>
remote <replaceable>172.16.0.1</replaceable>
}
}</programlisting>
<para>For more advanced configuration, refer to
&man.hast.conf.5;.</para>
<tip>
<para>It is also possible to use host names in the
<literal>remote</literal> statements if the hosts are
resolvable and defined either in
<filename>/etc/hosts</filename> or in the local
<acronym>DNS</acronym>.</para>
</tip>
<para>Once the configuration exists on both nodes, the
<acronym>HAST</acronym> pool can be created. Run these
commands on both nodes to place the initial metadata onto the
local disk and to start &man.hastd.8;:</para>
<screen>&prompt.root; <userinput>hastctl create <replaceable>test</replaceable></userinput>
&prompt.root; <userinput>service hastd onestart</userinput></screen>
<note>
<para>It is <emphasis>not</emphasis> possible to use
<acronym>GEOM</acronym>
providers with an existing file system or to convert an
existing storage to a <acronym>HAST</acronym>-managed pool.
This procedure needs to store some metadata on the provider
and there will not be enough required space available on an
existing provider.</para>
</note>
<para>A HAST node's <literal>primary</literal> or
<literal>secondary</literal> role is selected by an
administrator, or software like
<application>Heartbeat</application>, using &man.hastctl.8;.
On the primary node, <literal>hasta</literal>, issue this
command:</para>
<screen>&prompt.root; <userinput>hastctl role primary <replaceable>test</replaceable></userinput></screen>
<para>Run this command on the secondary node,
<literal>hastb</literal>:</para>
<screen>&prompt.root; <userinput>hastctl role secondary <replaceable>test</replaceable></userinput></screen>
<para>Verify the result by running <command>hastctl</command> on
each node:</para>
<screen>&prompt.root; <userinput>hastctl status <replaceable>test</replaceable></userinput></screen>
<para>Check the <literal>status</literal> line in the output.
If it says <literal>degraded</literal>, something is wrong
with the configuration file. It should say
<literal>complete</literal> on each node, meaning that the
synchronization between the nodes has started. The
synchronization completes when <command>hastctl
status</command> reports 0 bytes of <literal>dirty</literal>
extents.</para>
<para>The next step is to create a file system on the
<acronym>GEOM</acronym> provider and mount it. This must be
done on the <literal>primary</literal> node. Creating the
file system can take a few minutes, depending on the size of
the hard drive. This example creates a <acronym>UFS</acronym>
file system on <filename>/dev/hast/test</filename>:</para>
<screen>&prompt.root; <userinput>newfs -U /dev/hast/<replaceable>test</replaceable></userinput>
&prompt.root; <userinput>mkdir /hast/<replaceable>test</replaceable></userinput>
&prompt.root; <userinput>mount /dev/hast/<replaceable>test</replaceable> <replaceable>/hast/test</replaceable></userinput></screen>
<para>Once the <acronym>HAST</acronym> framework is configured
properly, the final step is to make sure that
<acronym>HAST</acronym> is started automatically during
system boot. Add this line to
<filename>/etc/rc.conf</filename>:</para>
<programlisting>hastd_enable="YES"</programlisting>
<sect3>
<title>Failover Configuration</title>
<para>The goal of this example is to build a robust storage
system which is resistant to the failure of any given node.
If the primary node fails, the secondary node is there to
take over seamlessly, check and mount the file system, and
continue to work without missing a single bit of
data.</para>
<para>To accomplish this task, the Common Address Redundancy
Protocol (<acronym>CARP</acronym>) is used to provide for
automatic failover at the <acronym>IP</acronym> layer.
<acronym>CARP</acronym> allows multiple hosts on the same
network segment to share an <acronym>IP</acronym> address.
Set up <acronym>CARP</acronym> on both nodes of the cluster
according to the documentation available in <xref
linkend="carp"/>. In this example, each node will have
its own management <acronym>IP</acronym> address and a
shared <acronym>IP</acronym> address of
<replaceable>172.16.0.254</replaceable>. The primary
<acronym>HAST</acronym> node of the cluster must be the
master <acronym>CARP</acronym> node.</para>
<para>The <acronym>HAST</acronym> pool created in the previous
section is now ready to be exported to the other hosts on
the network. This can be accomplished by exporting it
through <acronym>NFS</acronym> or
<application>Samba</application>, using the shared
<acronym>IP</acronym> address
<replaceable>172.16.0.254</replaceable>. The only problem
which remains unresolved is an automatic failover should the
primary node fail.</para>
<para>In the event of <acronym>CARP</acronym> interfaces going
up or down, the &os; operating system generates a
&man.devd.8; event, making it possible to watch for state
changes on the <acronym>CARP</acronym> interfaces. A state
change on the <acronym>CARP</acronym> interface is an
indication that one of the nodes failed or came back online.
These state change events make it possible to run a script
which will automatically handle the HAST failover.</para>
<para>To catch state changes on the
<acronym>CARP</acronym> interfaces, add this configuration
to <filename>/etc/devd.conf</filename> on each node:</para>
<programlisting>notify 30 {
match "system" "IFNET";
match "subsystem" "carp0";
match "type" "LINK_UP";
action "/usr/local/sbin/carp-hast-switch master";
};
notify 30 {
match "system" "IFNET";
match "subsystem" "carp0";
match "type" "LINK_DOWN";
action "/usr/local/sbin/carp-hast-switch slave";
};</programlisting>
<note>
<para>If the systems are running &os;&nbsp;10 or higher,
replace <filename>carp0</filename> with the name of the
<acronym>CARP</acronym>-configured interface.</para>
</note>
<para>Restart &man.devd.8; on both nodes to put the new
configuration into effect:</para>
<screen>&prompt.root; <userinput>service devd restart</userinput></screen>
<para>When the specified interface state changes by going up
or down , the system generates a notification, allowing the
&man.devd.8; subsystem to run the specified automatic
failover script,
<filename>/usr/local/sbin/carp-hast-switch</filename>.
For further clarification about this configuration, refer to
&man.devd.conf.5;.</para>
<para>Here is an example of an automated failover
script:</para>
<programlisting>#!/bin/sh
# Original script by Freddie Cash &lt;fjwcash@gmail.com&gt;
# Modified by Michael W. Lucas &lt;mwlucas@BlackHelicopters.org&gt;
# and Viktor Petersson &lt;vpetersson@wireload.net&gt;
# The names of the HAST resources, as listed in /etc/hast.conf
resources="<replaceable>test</replaceable>"
# delay in mounting HAST resource after becoming master
# make your best guess
delay=3
# logging
log="local0.debug"
name="carp-hast"
# end of user configurable stuff
case "$1" in
master)
logger -p $log -t $name "Switching to primary provider for ${resources}."
sleep ${delay}
# Wait for any "hastd secondary" processes to stop
for disk in ${resources}; do
while $( pgrep -lf "hastd: ${disk} \(secondary\)" &gt; /dev/null 2&gt;&amp;1 ); do
sleep 1
done
# Switch role for each disk
hastctl role primary ${disk}
if [ $? -ne 0 ]; then
logger -p $log -t $name "Unable to change role to primary for resource ${disk}."
exit 1
fi
done
# Wait for the /dev/hast/* devices to appear
for disk in ${resources}; do
for I in $( jot 60 ); do
[ -c "/dev/hast/${disk}" ] &amp;&amp; break
sleep 0.5
done
if [ ! -c "/dev/hast/${disk}" ]; then
logger -p $log -t $name "GEOM provider /dev/hast/${disk} did not appear."
exit 1
fi
done
logger -p $log -t $name "Role for HAST resources ${resources} switched to primary."
logger -p $log -t $name "Mounting disks."
for disk in ${resources}; do
mkdir -p /hast/${disk}
fsck -p -y -t ufs /dev/hast/${disk}
mount /dev/hast/${disk} /hast/${disk}
done
;;
slave)
logger -p $log -t $name "Switching to secondary provider for ${resources}."
# Switch roles for the HAST resources
for disk in ${resources}; do
if ! mount | grep -q "^/dev/hast/${disk} on "
then
else
umount -f /hast/${disk}
fi
sleep $delay
hastctl role secondary ${disk} 2&gt;&amp;1
if [ $? -ne 0 ]; then
logger -p $log -t $name "Unable to switch role to secondary for resource ${disk}."
exit 1
fi
logger -p $log -t $name "Role switched to secondary for resource ${disk}."
done
;;
esac</programlisting>
<para>In a nutshell, the script takes these actions when a
node becomes master:</para>
<itemizedlist>
<listitem>
<para>Promotes the <acronym>HAST</acronym> pool to
primary on the other node.</para>
</listitem>
<listitem>
<para>Checks the file system under the
<acronym>HAST</acronym> pool.</para>
</listitem>
<listitem>
<para>Mounts the pool.</para>
</listitem>
</itemizedlist>
<para>When a node becomes secondary:</para>
<itemizedlist>
<listitem>
<para>Unmounts the <acronym>HAST</acronym> pool.</para>
</listitem>
<listitem>
<para>Degrades the <acronym>HAST</acronym> pool to
secondary.</para>
</listitem>
</itemizedlist>
<caution>
<para>This is just an example script which serves as a proof
of concept. It does not handle all the possible scenarios
and can be extended or altered in any way, for example, to
start or stop required services.</para>
</caution>
<tip>
<para>For this example, a standard <acronym>UFS</acronym>
file system was used. To reduce the time needed for
recovery, a journal-enabled <acronym>UFS</acronym> or
<acronym>ZFS</acronym> file system can be used
instead.</para>
</tip>
<para>More detailed information with additional examples can
be found at <link
xlink:href="http://wiki.FreeBSD.org/HAST">http://wiki.FreeBSD.org/HAST</link>.</para>
</sect3>
</sect2>
<sect2>
<title>Troubleshooting</title>
<para><acronym>HAST</acronym> should generally work without
issues. However, as with any other software product, there
may be times when it does not work as supposed. The sources
of the problems may be different, but the rule of thumb is to
ensure that the time is synchronized between the nodes of the
cluster.</para>
<para>When troubleshooting <acronym>HAST</acronym>, the
debugging level of &man.hastd.8; should be increased by
starting <command>hastd</command> with <literal>-d</literal>.
This argument may be specified multiple times to further
increase the debugging level. Consider also using
<literal>-F</literal>, which starts <command>hastd</command>
in the foreground.</para>
<sect3 xml:id="disks-hast-sb">
<title>Recovering from the Split-brain Condition</title>
<para><firstterm>Split-brain</firstterm> occurs when the nodes
of the cluster are unable to communicate with each other,
and both are configured as primary. This is a dangerous
condition because it allows both nodes to make incompatible
changes to the data. This problem must be corrected
manually by the system administrator.</para>
<para>The administrator must decide which node has more
important changes or merge them manually. Then, let
<acronym>HAST</acronym> perform full synchronization of the
node which has the broken data. To do this, issue these
commands on the node which needs to be
resynchronized:</para>
<screen>&prompt.root; <userinput>hastctl role init <replaceable>test</replaceable></userinput>
&prompt.root; <userinput>hastctl create <replaceable>test</replaceable></userinput>
&prompt.root; <userinput>hastctl role secondary <replaceable>test</replaceable></userinput></screen>
</sect3>
</sect2>
</sect1>
</chapter>
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