os/doc
3
0
Fork 0
Code Issues Pull requests Projects Releases Wiki Activity

Add a chapter on file systems, currently covers ZFS with single disks and

Browse source 
RAIDZ configurations.  My intention is to eventually make this chapter a
complete resource for users who transfer files between, say, OSX, Windows,
and FreeBSD via external storage devices.  But those sections are just
stubs right now, and this chapter is not yet connected to the build.

Reviewed by:	keramida, pgj, manolis, remko
This commit is contained in:
Tom Rhodes 2008-09-28 12:06:24 +00:00
parent a8e6fa3372
commit 02c59cb128
Notes: svn2git 2020-12-08 03:00:23 +00:00 
svn path=/head/; revision=32971
2 changed files with 634 additions and 0 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

15
en_US.ISO8859-1/books/handbook/filesystems/Makefile Normal file
View file

@ -0,0 +1,15 @@
#
# Build the Handbook with just the content from this chapter.
#
# $FreeBSD$
#
CHAPTERS= filesystems/chapter.sgml
VPATH= ..
MASTERDOC= ${.CURDIR}/../${DOC}.${DOCBOOKSUFFIX}
DOC_PREFIX?= ${.CURDIR}/../../../..
.include "../Makefile"

619
en_US.ISO8859-1/books/handbook/filesystems/chapter.sgml Normal file
View file

@ -0,0 +1,619 @@
<!--
The FreeBSD Documentation Project
$FreeBSD$
-->
<chapter id="filesystems">
<chapterinfo>
<authorgroup>
<author>
<firstname>Tom</firstname>
<surname>Rhodes</surname>
<contrib>Written by </contrib>
</author>
</authorgroup>
</chapterinfo>
<title>File Systems Support</title>
<sect1 id="filesystems-synopsis">
<title>Synopsis</title>
<indexterm><primary>File Systems</primary></indexterm>
<indexterm>
<primary>File Systems Support</primary>
<see>File Systems</see>
</indexterm>
<para>File systems are an integral part of any operating system.
They allow for users to upload and store files, provide access
to data, and of course, make hard drives useful. Different
operating systems usually have one major aspect in common, that
is their native file system. On &os; this file system is known
as the Fast File System or <acronym>FFS</acronym> which is built
on the original Unix&trade; File System, also known as
<acronym>UFS</acronym>. This is the native file system on &os;
which is placed on hard disks for access to data.</para>
<para>&os; also supports a multitude of different file systems to
provide support for accessing data from other operating systems
locally, i.e.&nbsp;data stored on locally attached
<acronym>USB</acronym> storage devices, flash drives, and hard
disks. There is also support for some non-native file systems.
These are file systems developed on other
operating systems, like the &linux; Extended File System
(<acronym>EXT</acronym>), and the &sun; Z File System
(<acronym>ZFS</acronym>).</para>
<para>There are different levels of support for the various file
systems in &os;. Some will require a kernel module to be loaded,
others may require a toolset to be installed. This chapter is
designed to help users of &os; access other file systems on their
systems, starting with the &sun; Z file
system.</para>
<para>After reading this chapter, you will know:</para>
<itemizedlist>
<listitem>
<para>The difference between native and supported file systems.</para>
</listitem>
<listitem>
<para>What file systems are supported by &os;.</para>
</listitem>
<listitem>
<para>How to enable, configure, access and make use of
non-native file systems.</para>
</listitem>
</itemizedlist>
<para>Before reading this chapter, you should:</para>
<itemizedlist>
<listitem>
<para>Understand &unix; and &os; basics
(<xref linkend="basics">).</para>
</listitem>
<listitem>
<para>Be familiar with
the basics of kernel configuration/compilation
(<xref linkend="kernelconfig">).</para>
</listitem>
<listitem>
<para>Feel comfortable installing third party software
in &os; (<xref linkend="ports">).</para>
</listitem>
<listitem>
<para>Have some familiarity with disks, storage and
device names in &os; (<xref linkend="disks">).</para>
</listitem>
</itemizedlist>
<!--
Temporary warning to avoid listing experimental versions
and production versions of FreeBSD with this technology.
-->
<warning>
<para>The <acronym>ZFS</acronym> feature is considered
experimental. Some options may be lacking in functionality,
other parts may not work at all. In time, this feature will
be considered production ready and this documentation will be
altered to fit that situation.</para>
</warning>
</sect1>
<sect1 id="filesystems-zfs">
<title>The Z File System</title>
<para>The Z&nbsp;file system, developed by &sun;, is a new
technology designed to use a pooled storage method. This means
that space is only used as it is needed for data storage. It
has also been designed for maximum data integrity, supporting
data snapshots, multiple copies, and data checksums. A new
data replication model, known as <acronym>RAID</acronym>-Z has
been added. The <acronym>RAID</acronym>-Z model is similar
to <acronym>RAID</acronym>5 but is designed to prevent data
write corruption.</para>
<sect2>
<title>ZFS Tuning</title>
<para>The <acronym>ZFS</acronym> subsystem utilizes much of
the system resources, so some tuning may be required to provide
maximum efficiency during every-day use. As an experimental
feature in &os; this may change in the near future; however,
at this time, the following steps are recommended.</para>
<sect3>
<title>Memory</title>
<para>The total system memory should be at least one gigabyte,
with two gigabytes or more recommended. In all of the
examples here, the system has one gigabyte of memory with
several other tuning mechanisms in place.</para>
<para>Some people have had luck using fewer than one gigabyte
of memory, but with such a limited amount of physical memory,
when the system is under heavy load, it is very plausible
that &os; will panic due to memory exhaustion.</para>
</sect3>
<sect3>
<title>Kernel Configuration</title>
<para>It is recommended that unused drivers and options
be removed from the kernel configuration file. Since most
devices are available as modules, they may simply be loaded
using the <filename>/boot/loader.conf</filename> file.</para>
<para>Users of the i386 architecture should add the following
option to their kernel configuration file, rebuild their
kernel, and reboot:</para>
<programlisting>options KVA_PAGES=512</programlisting>
<para>This option will expand the kernel address space, thus
allowing the <varname>vm.kvm_size</varname> tunable to be
pushed beyond the currently imposed limit of 1&nbsp;GB
(2&nbsp;GB for <acronym>PAE</acronym>). To find the most
suitable value for this option, divide the desired address
space in megabytes by four (4). In this case, it is
<literal>512</literal> for 2&nbsp;GB.</para>
</sect3>
<sect3>
<title>Loader Tunables</title>
<para>The <devicename>kmem</devicename> address space should be
increased on all &os; architectures. On the test system with
one gigabyte of physical memory, success was achieved with the
following options which should be placed in
the <filename>/boot/loader.conf</filename> file and the system
restarted:</para>
<programlisting>vm.kmem_slze="330M"
vm.kmem_size_max="330M"
vfs.zfs.arc_max="40M"
vfs.zfs.vdev.cache.size="5M"</programlisting>
<para>For a more detailed list of recommendations for ZFS-related
tuning, see
<ulink url="http://wiki.freebsd.org/ZFSTuningGuide"></ulink>.</para>
</sect3>
</sect2>
<sect2>
<title>Using <acronym>ZFS</acronym></title>
<para>There is a start up mechanism that allows &os; to
mount <acronym>ZFS</acronym> pools during system
initialization. To set it, issue the following
commands:</para>
<screen>&prompt.root; <userinput>echo 'zfs_enable="YES"' &gt;&gt; /etc/rc.conf</userinput>
&prompt.root; <userinput>/etc/rc.d/zfs start</userinput></screen>
<para>The remainder of this document assumes two
<acronym>SCSI</acronym> disks are available, and their device names
are <devicename><replaceable>da0</replaceable></devicename>
and <devicename><replaceable>da1</replaceable></devicename>
respectively. Users of <acronym>IDE</acronym> hardware may
use the <devicename><replaceable>ad</replaceable></devicename>
devices in place of <acronym>SCSI</acronym> hardware.</para>
<sect3>
<title>Single Disk Pool</title>
<para>To create a <acronym>ZFS</acronym> over a single disk
device, use the <command>zpool</command> command:</para>
<screen>&prompt.root; <userinput>zpool create example /dev/da0</userinput></screen>
<para>To view the new pool, review the output of the
<command>df</command>:</para>
<screen>&prompt.root; <userinput>df</userinput>
Filesystem 1K-blocks Used Avail Capacity Mounted on
/dev/ad0s1a 2026030 235230 1628718 13% /
devfs 1 1 0 100% /dev
/dev/ad0s1d 54098308 1032846 48737598 2% /usr
example 17547136 0 17547136 0% /example</screen>
<para>This output clearly shows the <literal>example</literal>
pool has not only been created but
<emphasis>mounted</emphasis> as well. It is also accessible
just like a normal file system, files may be created on it
and users are able to browse it as in the
following example:</para>
<screen>&prompt.root <userinput>cd /example</userinput>
&prompt.root; <userinput>ls</userinput>
&prompt.root; <userinput>touch testfile</userinput>
&prompt.root; <userinput>ls -al</userinput>
total 4
drwxr-xr-x 2 root wheel 3 Aug 29 23:15 .
drwxr-xr-x 21 root wheel 512 Aug 29 23:12 ..
-rw-r--r-- 1 root wheel 0 Aug 29 23:15 testfile</screen>
<para>Unfortunately this pool is not taking advantage of
any <acronym>ZFS</acronym> features. Create a file system
on this pool, and enable compression on it:</para>
<screen>&prompt.root; <userinput>zfs create example/compressed</userinput>
&prompt.root; <userinput>zfs set compression=gzip example/compressed</userinput></screen>
<para>The <literal>example/compressed</literal> is now a
<acronym>ZFS</acronym> compressed file system. Try copying
some large files to it by copying them to
<filename class="directory">/example/compressed</filename>.</para>
<para>The compression may now be disabled with:</para>
<screen>&prompt.root; <userinput>zfs set compression=off example/compressed</userinput></screen>
<para>To unmount the file system, issue the following command
and then verify by using the <command>df</command>
utility:</para>
<screen>&prompt.root; <userinput>zfs umount example/compressed</userinput>
&prompt.root; <userinput>df</userinput>
Filesystem 1K-blocks Used Avail Capacity Mounted on
/dev/ad0s1a 2026030 235232 1628716 13% /
devfs 1 1 0 100% /dev
/dev/ad0s1d 54098308 1032864 48737580 2% /usr
example 17547008 0 17547008 0% /example</screen>
<para>Re-mount the file system to make it accessible
again, and verify with <command>df</command>:</para>
<screen>&prompt.root; <userinput>zfs mount example/compressed</userinput>
&prompt.root; <userinput>df</userinput>
Filesystem 1K-blocks Used Avail Capacity Mounted on
/dev/ad0s1a 2026030 235234 1628714 13% /
devfs 1 1 0 100% /dev
/dev/ad0s1d 54098308 1032864 48737580 2% /usr
example 17547008 0 17547008 0% /example
example/compressed 17547008 0 17547008 0% /example/compressed</screen>
<para>The pool and file system may also be observed by viewing
the output from <command>mount</command>:</para>
<screen>&prompt.root; <userinput>mount</userinput>
/dev/ad0s1a on / (ufs, local)
devfs on /dev (devfs, local)
/dev/ad0s1d on /usr (ufs, local, soft-updates)
example on /example (zfs, local)
example/data on /example/data (zfs, local)
example/compressed on /example/compressed (zfs, local)</screen>
<para>As observed, <acronym>ZFS</acronym> file systems, after
creation, may be used like ordinary file systems; however,
many other features are also available. In the following
example, a new file system, <literal>data</literal> is
created. Important files will be stored here, so the file
system is set to keep two copies of each data block:</para>
<screen>&prompt.root; <userinput>zfs create example/data</userinput>
&prompt.root; <userinput>zfs set copies=2 example/data</userinput></screen>
<para>It is now possible to see the data and space utilization
by issuing the <command>df</command> again:</para>
<screen>&prompt.root; <userinput>df</userinput>
Filesystem 1K-blocks Used Avail Capacity Mounted on
/dev/ad0s1a 2026030 235234 1628714 13% /
devfs 1 1 0 100% /dev
/dev/ad0s1d 54098308 1032864 48737580 2% /usr
example 17547008 0 17547008 0% /example
example/compressed 17547008 0 17547008 0% /example/compressed
example/data 17547008 0 17547008 0% /example/data</screen>
<para>Notice that each file system on the pool has the same
amount of available space. This is the reason for using
the <command>df</command> through these examples, to show
that the file systems are using only the amount of space
they need and will all draw from the same pool.
The <acronym>ZFS</acronym> file system does away with concepts
such as volumes and partitions, and allows for several file
systems to occupy the same pool. Destroy the file systems,
and then destroy the pool as they are no longer
needed:</para>
<screen>&prompt.root; <userinput>zfs destroy example/compressed</userinput>
&prompt.root; <userinput>zfs destroy example/data</userinput>
&prompt.root; <userinput>zpool destroy example</userinput></screen>
<para>Disks go bad and fail, an unavoidable trait. When
this disk goes bad, the data will be lost. One method of
avoiding data loss due to a failed hard disk is to implement
a <acronym>RAID</acronym>. <acronym>ZFS</acronym> supports
this feature in its pool design which is covered in
the next section.</para>
</sect3>
<sect3>
<title><acronym>ZFS</acronym> RAID-Z</title>
<para>As previously noted, this section will assume that
two <acronym>SCSI</acronym> exists as devices
<devicename>da0</devicename> and
<devicename>da1</devicename>. To create a
<acronym>RAID</acronym>-Z pool, issue the following
command:</para>
<screen>&prompt.root; <userinput>zpool create storage raidz da0 da1</userinput></screen>
<para>The <literal>storage</literal> zpool should have been
created. This may be verified by using the &man.mount.8; and
&man.df.1; commands as before. More disk devices may have
been allocated by adding them to the end of the list above.
Make a new file system in the pool, called
<literal>home</literal> where user files will eventually be
placed:</para>
<screen>&prompt.root; <userinput>zfs create storage/home</userinput></screen>
<para>It is now possible to enable compression and keep extra
copies of the user's home directories and files. This may
be accomplished just as before using the following
commands:</para>
<screen>&prompt.root; <userinput>zfs set copies=2 storage/home</userinput>
&prompt.root; <userinput>zfs set compression=gzip storage/home</userinput></screen>
<para>To make this the new home directory for users, copy the
user data to this directory, and create the appropriate
symbolic links:</para>
<screen>&prompt.root; <userinput>cp -rp /home/* /storage/home</userinput>
&prompt.root; <userinput>rm -rf /home /usr/home</userinput>
&prompt.root; <userinput>ln -s /storage/home /home</userinput>
&prompt.root; <userinput>ln -s /storage/home /usr/home</userinput></screen>
<para>Users should now have their data stored on the freshly
created <filename class="directory">/storage/home</filename>
file system. Test by adding a new user and logging in as
that user.</para>
<para>Try creating a snapshot which may be rolled back
later:</para>
<screen>&prompt.root; <userinput>zfs snapshot storage/home@08-30-08</userinput></screen>
<para>Note that the snapshot option will only capture a real
file system, not a home directory or a file. The
<literal>@</literal> character is a delimiter used between
the file system name or the volume name. when a user's
home directory gets trashed, restore it with:</para>
<screen>&prompt.root; <userinput>zfs rollback storage/home@08-30-08</userinput></screen>
<para>To get a list of all available snapshots, run the
<command>ls</command> in the file system's
<filename class="directory">.zfs/snapshot</filename>
directory. For example, to see the previously taken
snapshot, perform the following command:</para>
<screen>&prompt.root; <userinput>ls /storage/home/.zfs/snapshot</userinput></screen>
<para>It is possible to write a script to perform monthly
snapshots on user data; however, over time, snapshots
may consume a great deal of disk space. The previous
snapshot may be removed using the following command:</para>
<screen>&prompt.root; <userinput>zfs destroy storage/home@08-30-08</userinput></screen>
<para>There is no reason, after all of this testing, we should
keep <filename class="directory">/storage/home</filename>
around in its present state. Make it the real
<filename class="directory">/home</filename> file
system:</para>
<screen>&prompt.root; <userinput>zfs set mountpoint=/home storage/home</userinput></screen>
<para>Issuing the <command>df</command> and
<command>mount</command> commands will show that the system
now treats our file system as the real
<filename class="directory">/home</filename>:</para>
<screen>&prompt.root; <userinput>mount</userinput>
/dev/ad0s1a on / (ufs, local)
devfs on /dev (devfs, local)
/dev/ad0s1d on /usr (ufs, local, soft-updates)
storage on /storage (zfs, local)
storage/home on /home (zfs, local)
&prompt.root; <userinput>df</userinput>
Filesystem 1K-blocks Used Avail Capacity Mounted on
/dev/ad0s1a 2026030 235240 1628708 13% /
devfs 1 1 0 100% /dev
/dev/ad0s1d 54098308 1032826 48737618 2% /usr
storage 17547008 0 17547008 0% /storage
storage/home 17547008 0 17547008 0% /home</screen>
<para>This completes the <acronym>RAID</acronym>-Z
configuration. To get status updates about the file systems
created during the nightly &man.periodic.8; runs, issue the
following command:</para>
<screen>&prompt.root; <userinput>echo 'daily_status_zfs_enable="YES"' &gt;&gt; /etc/periodic.conf</userinput></screen>
</sect3>
<sect3>
<title>Recovering <acronym>RAID</acronym>-Z</title>
<para>Every software <acronym>RAID</acronym> has a method of
monitoring their <literal>state</literal>.
<acronym>ZFS</acronym> is no exception. The status of
<acronym>RAID</acronym>-Z devices may be viewed with the
following command:</para>
<screen>&prompt.root; <userinput>zpool status -x</userinput></screen>
<para>If all pools are healthy and everything is normal, the
following message will be returned:</para>
<screen>all pools are healthy</screen>
<para>If there is an issue, perhaps a disk has gone offline,
the pool state will be returned and look similar to:</para>
<screen> pool: storage
state: DEGRADED
status: One or more devices has been taken offline by the administrator.
Sufficient replicas exist for the pool to continue functioning in a
degraded state.
action: Online the device using 'zpool online' or replace the device with
'zpool replace'.
scrub: none requested
config:
NAME STATE READ WRITE CKSUM
storage DEGRADED 0 0 0
raidz1 DEGRADED 0 0 0
da0 ONLINE 0 0 0
da1 OFFLINE 0 0 0
errors: No known data errors</screen>
<para>This states that the device was taken offline by the
administrator. This is true for this particular example.
To take the disk offline, the following command was
used:</para>
<screen>&prompt.root; <userinput>zpool offline storage da1</userinput></screen>
<para>It is now possible to replace the
<devicename>da1</devicename> after the system has been
powered down. When the system is back online, the following
command may issued to replace the disk:</para>
<screen>&prompt.root; <userinput>zpool replace storage da1</userinput></screen>
<para>From here, the status may be checked again, this time
without the <option>-x</option> flag to get state
information:</para>
<screen>&prompt.root; <userinput>zpool status storage</userinput>
pool: storage
state: ONLINE
scrub: resilver completed with 0 errors on Sat Aug 30 19:44:11 2008
config:
NAME STATE READ WRITE CKSUM
storage ONLINE 0 0 0
raidz1 ONLINE 0 0 0
da0 ONLINE 0 0 0
da1 ONLINE 0 0 0
errors: No known data errors</screen>
<para>As shown from this example, everything appears to be
normal.</para>
</sect3>
<sect3>
<title>Data Verification</title>
<para>As previously mentioned, <acronym>ZFS</acronym> uses
<literal>checksums</literal> to verify the integrity of
stored data. They are enabled automatically upon creation
of file systems and may be disabled using the following
command:</para>
<screen>&prompt.root; <userinput>zfs set checksum=off storage/home</userinput></screen>
<para>This is not a wise idea; however, as checksums take
very little storage space and are more useful enabled. There
also appear to be no noticeable costs having them enabled.
While enabled, it is possible to have <acronym>ZFS</acronym>
check data integrity using checksum verification. This
process is known as <quote>scrubing.</quote> To verify the
data integrity of the <literal>storage</literal> pool, issue
the following command:</para>
<screen>&prompt.root; <userinput>zpool scrub storage</userinput></screen>
<para>This process may take considerable time depending on
the amount of data stored. It is also very
<acronym>I/O</acronym> intensive, so much that only one
of these operations may be run at any given time. After
the scrub has completed, the status is updated and may be
viewed by issuing a status request:</para>
<screen>&prompt.root; <userinput>zpool status storage</userinput>
pool: storage
state: ONLINE
scrub: scrub completed with 0 errors on Sat Aug 30 19:57:37 2008
config:
NAME STATE READ WRITE CKSUM
storage ONLINE 0 0 0
raidz1 ONLINE 0 0 0
da0 ONLINE 0 0 0
da1 ONLINE 0 0 0
errors: No known data errors</screen>
<para>The completion time is in plain view in this example.
This feature helps to ensure data integrity over a long
period of time.</para>
<para>There are many more options for the Z&nbsp;file system,
reading the &man.zfs.1; and &man.zpool.1; manual
pages.</para>
</sect3>
</sect2>
</sect1>
<!--
XXXTR: stub sections (added later, as needed, as desire,
after I get opinions from -doc people):
Still need to discuss native and foreign file systems.
<sect1>
<title>Device File System</title>
</sect1>
<sect1>
<title>DOS and NTFS File Systems</title>
<para>This is a good section for those who transfer files, using
USB devices, from Windows to FreeBSD and vice-versa. My camera,
and many other cameras I have seen default to using FAT16. There
is (was?) a kde utility, I think called kamera, that could be used
to access camera devices. A section on this would be useful.</para>
<para>XXXTR: Though! The disks chapter, covers a bit of this and
devfs under it's USB devices. It leaves a lot to be desired though,
see:
http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/usb-disks.html
It may be better to flesh out that section a bit more. Add the
word "camera" to it so that others can easily notice.</para>
</sect1>
<sect1>
<title>Linux EXT File System</title>
<para>Probably NOT as useful as the other two, but it requires
knowledge of the existence of the tools. Which are hidden in
the ports collection. Most Linux guys would probably only use
Linux, BSD guys would be smarter and use NFS.</para>
</sect1>
<sect1>
<title>HFS</title>
<para>I think this is the file system used on Apple OSX. There are
tools in the ports collection, and with Apple being a big
FreeBSD supporter and user of our technologies, surely there
is enough cross over to cover this?</para>
</sect1>
-->
</chapter>