Rework the gmirror section to create mirrors properly. The second half
of this new section was written by Hiroki Sato.
This commit is contained in:
Warren Block
parent
0e8f52f505
commit
dc068cb25d
Notes:
svn2git
2020-12-08 03:00:23 +00:00
svn path=/head/; revision=39909
1 changed files with 555 additions and 167 deletions
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@ -234,210 +234,598 @@ Done.</screen>
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<indexterm>
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<primary>Disk Mirroring</primary>
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</indexterm>
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<indexterm>
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<primary>RAID1</primary>
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</indexterm>
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<para>Mirroring is a technology used by many corporations and home
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users to back up data without interruption. When a mirror
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exists, it simply means that diskB replicates diskA. Or,
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perhaps diskC+D replicates diskA+B. Regardless of the disk
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configuration, the important aspect is that information on one
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disk or partition is being replicated. Later, that information
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could be more easily restored, backed up without causing service
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or access interruption, and even be physically stored in a data
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safe.</para>
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<para><acronym>RAID1</acronym>, or
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<firstterm>mirroring</firstterm>, is the technique of writing
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the same data to more than one disk drive. Mirrors are usually
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used to guard against data loss due to drive failure. Each
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drive in a mirror contains an identical copy of the data. When
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an individual drive fails, the mirror continues to work,
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providing data from the drives that are still functioning. The
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computer keeps running, and the administrator has time to
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replace the failed drive without user interruption.</para>
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<para>To begin, ensure the system has two disk drives of equal
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size, these exercises assume they are direct access (&man.da.4;)
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<acronym>SCSI</acronym> disks.</para>
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<para>Two common situations are illustrated in these examples.
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The first is creating a mirror out of two new drives and using
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it as a replacement for an existing single drive. The second
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example creates a mirror on a single new drive, copies the old
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drive's data to it, then inserts the old drive into the
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mirror. While this procedure is slightly more complicated, it
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only requires one new drive.</para>
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<sect2>
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<title>Mirroring Primary Disks</title>
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<para>Traditionally, the two drives in a mirror are identical in
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model and capacity, but &man.gmirror.8; does not require that.
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Mirrors created with dissimilar drives will have a capacity
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equal to that of the smallest drive in the mirror. Extra space
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on larger drives will be unused. Drives inserted into the
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mirror later must have at least as much capacity as the smallest
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drive already in the mirror.</para>
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<para>Assuming &os; has been installed on the first,
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<devicename>da0</devicename> disk device, &man.gmirror.8;
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should be told to store its primary data there.</para>
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<warning>
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<para>The mirroring procedures shown here are non-destructive,
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but as with any major disk operation, make a full backup
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first.</para>
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</warning>
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<para>Before building the mirror, enable additional debugging
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information and opening access to the device by setting the
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<varname>kern.geom.debugflags</varname> &man.sysctl.8; option
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to the following value:</para>
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<sect2 id="GEOM-mirror-metadata">
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<title>Metadata Issues</title>
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<screen>&prompt.root; <userinput>sysctl kern.geom.debugflags=17</userinput></screen>
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<para>Many disk systems store metadata at the end of each disk.
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Old metadata should be erased before reusing the disk for a
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mirror. Most problems are caused by two particular types of
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leftover metadata: GPT partition tables, and old
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&man.gmirror.8; metadata from a previous mirror.</para>
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<para>Now create the mirror. Begin the process by storing
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meta-data information on the primary disk device,
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effectively creating the
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<filename class="devicefile">/dev/mirror/gm</filename> device
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using the following command:</para>
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<para>GPT metadata can be erased with &man.gpart.8;. This
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example erases both primary and backup GPT partition tables
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from disk <devicename>ada8</devicename>:</para>
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<warning>
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<para>Creating a mirror out of the boot drive may result in
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data loss if any data has been stored on the last sector of
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the disk. This risk is reduced if creating the mirror is
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done promptly after a fresh install of &os;. The following
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procedure is also incompatible with the default installation
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settings of &os; 9.<replaceable>X</replaceable> which
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use the new <acronym>GPT</acronym> partition scheme. GEOM
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will overwrite <acronym>GPT</acronym> metadata, causing data
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loss and possibly an unbootable system.</para>
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</warning>
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<screen>&prompt.root; <userinput>gpart destroy -F ada8</userinput></screen>
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<screen>&prompt.root; <userinput>gmirror label -vb round-robin gm0 /dev/da0</userinput></screen>
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<para>&man.gmirror.8; can remove a disk from an active mirror
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and erase the metadata in one step. Here, the example disk
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<devicename>ada8</devicename> is removed from the active
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mirror <devicename>gm4</devicename>:</para>
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<para>The system should respond with:</para>
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<screen>&prompt.root; <userinput>gmirror remove gm4 ada8</userinput></screen>
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<screen>Metadata value stored on /dev/da0.
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Done.</screen>
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<para>If the mirror is not running but old mirror metadata is
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still on the disk, use <command>gmirror clear</command> to
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remove it:</para>
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<para>Initialize GEOM, this will load the
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<filename>/boot/kernel/geom_mirror.ko</filename> kernel
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module:</para>
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<screen>&prompt.root; <userinput>gmirror clear ada8</userinput></screen>
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<screen>&prompt.root; <userinput>gmirror load</userinput></screen>
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<note>
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<para>When this command completes successfully, it creates the
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<devicename>gm0</devicename> device node under the
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<filename class="directory">/dev/mirror</filename>
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directory.</para>
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</note>
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<para>Enable loading of the <filename>geom_mirror.ko</filename>
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kernel module during system initialization:</para>
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<screen>&prompt.root; <userinput>echo 'geom_mirror_load="YES"' >> /boot/loader.conf</userinput></screen>
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<para>Edit the <filename>/etc/fstab</filename> file, replacing
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references to the old <devicename>da0</devicename> with the
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new device nodes of the <devicename>gm0</devicename> mirror
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device.</para>
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<note>
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<para>If &man.vi.1; is your preferred editor, the following is
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an easy way to accomplish this task:</para>
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<screen>&prompt.root; <userinput>vi /etc/fstab</userinput></screen>
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<para>In &man.vi.1; back up the current contents of
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<filename>fstab</filename> by typing
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<userinput>:w /etc/fstab.bak</userinput>. Then
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replace all old <devicename>da0</devicename> references
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with <devicename>gm0</devicename> by typing
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<userinput>:%s/da/mirror\/gm/g</userinput>.</para>
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</note>
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<para>The resulting <filename>fstab</filename> file should look
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similar to the following. It does not matter if the disk
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drives are <acronym>SCSI</acronym> or <acronym>ATA</acronym>,
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the <acronym>RAID</acronym> device will be
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<devicename>gm</devicename> regardless.</para>
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<programlisting># Device Mountpoint FStype Options Dump Pass#
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/dev/mirror/gm0s1b none swap sw 0 0
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/dev/mirror/gm0s1a / ufs rw 1 1
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/dev/mirror/gm0s1d /usr ufs rw 0 0
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/dev/mirror/gm0s1f /home ufs rw 2 2
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#/dev/mirror/gm0s2d /store ufs rw 2 2
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/dev/mirror/gm0s1e /var ufs rw 2 2
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/dev/acd0 /cdrom cd9660 ro,noauto 0 0</programlisting>
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<para>Reboot the system:</para>
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<screen>&prompt.root; <userinput>shutdown -r now</userinput></screen>
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<para>During system initialization, the
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<devicename>gm0</devicename> should be used in place of the
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<devicename>da0</devicename> device. Once fully initialized,
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this may be checked by visually inspecting the output from
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the <command>mount</command> command:</para>
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<screen>&prompt.root; <userinput>mount</userinput>
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Filesystem 1K-blocks Used Avail Capacity Mounted on
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/dev/mirror/gm0s1a 1012974 224604 707334 24% /
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devfs 1 1 0 100% /dev
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/dev/mirror/gm0s1f 45970182 28596 42263972 0% /home
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/dev/mirror/gm0s1d 6090094 1348356 4254532 24% /usr
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/dev/mirror/gm0s1e 3045006 2241420 559986 80% /var
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devfs 1 1 0 100% /var/named/dev</screen>
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<para>The output looks good, as expected. Finally, to begin
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synchronization, insert the <devicename>da1</devicename> disk
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into the mirror using the following command:</para>
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<screen>&prompt.root; <userinput>gmirror insert gm0 /dev/da1</userinput></screen>
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<para>As the mirror is built the status may be checked using
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the following command:</para>
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<screen>&prompt.root; <userinput>gmirror status</userinput></screen>
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<para>Once the mirror has been built and all current data
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has been synchronized, the output from the above command
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should look like:</para>
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<screen> Name Status Components
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mirror/gm0 COMPLETE da0
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da1</screen>
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<para>If there are any issues, or the mirror is still
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completing the build process, the example will show
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<literal>DEGRADED</literal> in place of
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<literal>COMPLETE</literal>.</para>
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<para>&man.gmirror.8; stores one block of metadata at the end of
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the disk. Because GPT partition schemes also store metadata
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at the end of the disk, mirroring full GPT disks with
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&man.gmirror.8; is not recommended. MBR partitioning is used
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here because it only stores a partition table at the start of
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the disk and does not conflict with &man.gmirror.8;.</para>
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</sect2>
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<sect2>
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<title>Creating a Mirror with Two New Disks</title>
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<para>In this example, &os; has already been installed on a
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single disk, <devicename>ada0</devicename>. Two new disks,
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<devicename>ada1</devicename> and
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<devicename>ada2</devicename>, have been connected to the
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system. A new mirror will be created on these two disks and
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used to replace the old single disk.</para>
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<para>&man.gmirror.8; requires a kernel module,
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<filename>geom_mirror.ko</filename>, either built into the
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kernel or loaded at boot- or run-time. Manually load the
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kernel module now:</para>
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<screen>&prompt.root; <userinput>gmirror load</userinput></screen>
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<para>Create the mirror with the two new drives.</para>
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<screen>&prompt.root; <userinput>gmirror label -v gm0 /dev/ada1 /dev/ada2</userinput></screen>
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<para><devicename>gm0</devicename> is a user-chosen device name
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assigned to the new mirror. After the mirror has been
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started, this device name will appear in the
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<filename>/dev/mirror/</filename> directory.</para>
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<para>MBR and bsdlabel partition tables can now be created on
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the mirror with &man.gpart.8;. Here we show a traditional
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split-filesystem layout, with partitions for
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<filename>/</filename>, swap, <filename>/var</filename>,
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<filename>/tmp</filename>, and <filename>/usr</filename>. A
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single <filename>/</filename> filesystem and a swap partition
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will also work.</para>
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<para>Partitions on the mirror do not have to be the same size
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as those on the existing disk, but they must be large enough
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to hold all the data already present on
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<devicename>ada0</devicename>.</para>
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<screen>&prompt.root; <userinput>gpart create -s MBR mirror/gm0</userinput>
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&prompt.root; <userinput>gpart add -t -a 4kfreebsd mirror/gm0</userinput>
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&prompt.root; <userinput>gpart show mirror/gm0</userinput>
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=> 63 156301423 mirror/gm0 MBR (74G)
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63 63 - free - (31k)
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126 156301299 1 freebsd (74G)
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156301425 61 - free - (30k)</screen>
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<screen>&prompt.root; <userinput>gpart create -s BSD mirror/gm0s1</userinput>
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&prompt.root; <userinput>gpart add -t freebsd-ufs -a 4k -s 2g mirror/gm0s1</userinput>
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&prompt.root; <userinput>gpart add -t freebsd-swap -a 4k -s 4g mirror/gm0s1</userinput>
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&prompt.root; <userinput>gpart add -t freebsd-ufs -a 4k -s 2g mirror/gm0s1</userinput>
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&prompt.root; <userinput>gpart add -t freebsd-ufs -a 4k -s 1g mirror/gm0s1</userinput>
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&prompt.root; <userinput>gpart add -t freebsd-ufs -a 4k mirror/gm0s1</userinput>
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&prompt.root; <userinput>gpart show mirror/gm0s1</userinput>
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=> 0 156301299 mirror/gm0s1 BSD (74G)
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0 2 - free - (1.0k)
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2 4194304 1 freebsd-ufs (2.0G)
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4194306 8388608 2 freebsd-swap (4.0G)
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12582914 4194304 4 freebsd-ufs (2.0G)
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16777218 2097152 5 freebsd-ufs (1.0G)
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18874370 137426928 6 freebsd-ufs (65G)
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156301298 1 - free - (512B)</screen>
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<para>Make the mirror bootable by installing bootcode in the MBR
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and bsdlabel and setting the active slice:</para>
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<screen>&prompt.root; <userinput>gpart bootcode -b /boot/mbr mirror/gm0</userinput>
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&prompt.root; <userinput>gpart set -a active -i 1 mirror/gm0</userinput>
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&prompt.root; <userinput>gpart bootcode -b /boot/boot mirror/gm0s1</userinput></screen>
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<para>Format the filesystems on the new mirror, enabling
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soft-updates.</para>
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<screen>&prompt.root; <userinput>newfs -U /dev/mirror/gm0s1a</userinput>
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&prompt.root; <userinput>newfs -U /dev/mirror/gm0s1d</userinput>
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&prompt.root; <userinput>newfs -U /dev/mirror/gm0s1e</userinput>
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&prompt.root; <userinput>newfs -U /dev/mirror/gm0s1f</userinput></screen>
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<para>Filesystems from the original disk
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(<devicename>ada0</devicename>) can now be copied onto the
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mirror with &man.dump.8; and &man.restore.8;.</para>
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<screen>&prompt.root; <userinput>mount /dev/mirror/gm0s1a /mnt</userinput>
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&prompt.root; <userinput>dump -C16 -b64 -0aL -f - / | (cd /mnt && restore -rf -)</userinput>
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&prompt.root; <userinput>mount /dev/mirror/gm0s1d /mnt/var</userinput>
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&prompt.root; <userinput>mount /dev/mirror/gm0s1e /mnt/tmp</userinput>
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&prompt.root; <userinput>mount /dev/mirror/gm0s1f /mnt/usr</userinput>
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&prompt.root; <userinput>dump -C16 -b64 -0aL -f - /var | (cd /mnt/var && restore -rf -)</userinput>
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&prompt.root; <userinput>dump -C16 -b64 -0aL -f - /tmp | (cd /mnt/tmp && restore -rf -)</userinput>
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&prompt.root; <userinput>dump -C16 -b64 -0aL -f - /usr | (cd /mnt/usr && restore -rf -)</userinput></screen>
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<para><filename>/mnt/etc/fstab</filename> must be edited to
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point to the new mirror filesystems:</para>
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<programlisting># Device Mountpoint FStype Options Dump Pass#
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/dev/mirror/gm0s1a / ufs rw 1 1
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/dev/mirror/gm0s1b none swap sw 0 0
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/dev/mirror/gm0s1d /var ufs rw 2 2
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/dev/mirror/gm0s1e /tmp ufs rw 2 2
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/dev/mirror/gm0s1f /usr ufs rw 2 2</programlisting>
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<para>If the &man.gmirror.8; kernel module has not been built
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into the kernel, <filename>/mnt/boot/loader.conf</filename> is
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edited to load the module at boot:</para>
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<programlisting>geom_mirror_load="YES"</programlisting>
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<para>Reboot the system to test the new mirror and verify that
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all data has been copied. The BIOS will see the mirror as two
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individual drives rather than a mirror. Because the drives
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are identical, it does not matter which is selected to
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boot.</para>
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<para>See the
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<link linkend="gmirror-troubleshooting">Troubleshooting</link>
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section if there are problems booting. Powering down and
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disconnecting the original <devicename>ada0</devicename> disk
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will allow it to be kept as an offline backup.</para>
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<para>In use, the mirror will behave just like the original
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single drive.</para>
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</sect2>
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<sect2>
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||||
<title>Creating a Mirror with an Existing Drive</title>
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||||
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||||
<para>In this example, &os; has already been installed on a
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single disk, <devicename>ada0</devicename>. A new disk,
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<devicename>ada1</devicename>, has been connected to the
|
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system. A one-disk mirror will be created on the new disk,
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the existing system copied onto it, and then old disk will be
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inserted into the mirror. This slightly complex procedure is
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required because &man.gmirror.8; needs to put a 512-byte block
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of metadata at the end of each disk, and the existing
|
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<devicename>ada0</devicename> has usually had all of its space
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already allocated.</para>
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||||
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||||
<para>Load the &man.gmirror.8; kernel module.</para>
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<screen>&prompt.root; <userinput>gmirror load</userinput></screen>
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||||
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||||
<para>Check the media size of the original disk with
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&man.diskinfo.8;.</para>
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<screen>&prompt.root; <userinput>diskinfo -v ada0 | head -n3</userinput>
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/dev/ada0
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512 # sectorsize
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1000204821504 # mediasize in bytes (931G)</screen>
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<para>Create a mirror on the new disk. To make certain that the
|
||||
mirror capacity is not any larger than the original drive,
|
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&man.gnop.8; is used to create a fake drive of the exact same
|
||||
size. This drive does not store any data, but is used only to
|
||||
limit the size of the mirror. When &man.gmirror.8; creates
|
||||
the mirror, it will restrict the capacity to the size of
|
||||
<devicename>gzero.nop</devicename> even if the new drive
|
||||
(<devicename>ada1</devicename>) has more space. Note that the
|
||||
<replaceable>1000204821504</replaceable> in the second line
|
||||
should be equal to <devicename>ada0</devicename>'s media size
|
||||
as shown by &man.diskinfo.8; above.</para>
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||||
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<screen>&prompt.root; <userinput>geom zero load</userinput>
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&prompt.root; <userinput>gnop create -s 1000204821504 gzero</userinput>
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&prompt.root; <userinput>gmirror label -v gm0 gzero.nop ada1</userinput>
|
||||
&prompt.root; <userinput>gmirror forget gm0</userinput></screen>
|
||||
|
||||
<para><devicename>gzero.nop</devicename> does not store any
|
||||
data, so the mirror does not see it as connected. The mirror
|
||||
is told to <quote>forget</quote> unconnected components,
|
||||
removing references to <devicename>gzero.nop</devicename>.
|
||||
The result is a mirror device containing only a single disk,
|
||||
<devicename>ada1</devicename>.</para>
|
||||
|
||||
<para>After creating <devicename>gm0</devicename>, view the
|
||||
partition table on <devicename>ada0</devicename>.</para>
|
||||
|
||||
<para>This output is from a 1 TB drive. If there is some
|
||||
unallocated space at the end of the drive, the contents may be
|
||||
copied directly from <devicename>ada0</devicename> to the new
|
||||
mirror.</para>
|
||||
|
||||
<para>However, if the output shows that all of the space on the
|
||||
disk is allocated like the following listing, there is no
|
||||
space available for the 512-byte &man.gmirror.8; metadata at
|
||||
the end of the disk.</para>
|
||||
|
||||
<screen>&prompt.root; <userinput>gpart show ada0</userinput>
|
||||
=> 63 1953525105 ada0 MBR (931G)
|
||||
63 1953525105 1 freebsd [active] (931G)</screen>
|
||||
|
||||
<para>In this case, the partition table must be edited to reduce
|
||||
the capacity by one sector on
|
||||
<devicename>mirror/gm0</devicename>. The procedure will
|
||||
be explained later.</para>
|
||||
|
||||
<para>In either case, partition tables on the primary disk
|
||||
should be copied first. It can be done by using &man.gpart.8;
|
||||
<command>backup</command> and <command>restore</command>
|
||||
subcommands.</para>
|
||||
|
||||
<screen>&prompt.root; <userinput>gpart backup ada0 > table.ada0</userinput>
|
||||
&prompt.root; <userinput>gpart backup ada0s1 > table.ada0s1</userinput></screen>
|
||||
|
||||
<para>These commands create two files,
|
||||
<filename>table.ada0</filename> and
|
||||
<filename>table.ada0s1</filename>. This example is from a
|
||||
1 TB drive:</para>
|
||||
|
||||
<screen>&prompt.root; <userinput>cat table.ada0</userinput>
|
||||
MBR 4
|
||||
1 freebsd 63 1953525105 [active]</screen>
|
||||
|
||||
<screen>&prompt.root; <userinput>cat table.ada0s1</userinput>
|
||||
BSD 8
|
||||
1 freebsd-ufs 0 4194304
|
||||
2 freebsd-swap 4194304 33554432
|
||||
4 freebsd-ufs 37748736 50331648
|
||||
5 freebsd-ufs 88080384 41943040
|
||||
6 freebsd-ufs 130023424 838860800
|
||||
7 freebsd-ufs 968884224 984640881</screen>
|
||||
|
||||
<para>If the whole disk was used in the output of &man.gpart.8;
|
||||
<command>show</command>, the capacity in these partition
|
||||
tables must be reduced by one sector. Edit the two files,
|
||||
reducing the size of both the slice and last partition by one.
|
||||
These are the last numbers in each listing.</para>
|
||||
|
||||
<screen>&prompt.root; <userinput>cat table.ada0</userinput>
|
||||
MBR 4
|
||||
1 freebsd 63 <emphasis>1953525104</emphasis> [active]</screen>
|
||||
|
||||
<screen>&prompt.root; <userinput>cat table.ada0s1</userinput>
|
||||
BSD 8
|
||||
1 freebsd-ufs 0 4194304
|
||||
2 freebsd-swap 4194304 33554432
|
||||
4 freebsd-ufs 37748736 50331648
|
||||
5 freebsd-ufs 88080384 41943040
|
||||
6 freebsd-ufs 130023424 838860800
|
||||
7 freebsd-ufs 968884224 <emphasis>984640880</emphasis></screen>
|
||||
|
||||
<para>If at least one sector was unallocated at the end of the
|
||||
disk, these two files can be used without modification.</para>
|
||||
|
||||
<para>Now restore the partition table into
|
||||
<devicename>mirror/gm0</devicename>.</para>
|
||||
|
||||
<screen>&prompt.root; <userinput>gpart restore mirror/gm0 < table.ada0</userinput>
|
||||
&prompt.root; <userinput>gpart restore mirror/gm0s1 < table.ada0s1</userinput></screen>
|
||||
|
||||
<para>Check the partition table with the &man.gpart.8;
|
||||
<command>show</command>. This example has
|
||||
<devicename>gm0s1a</devicename> for <filename>/</filename>,
|
||||
<devicename>gm0s1d</devicename> for <filename>/var</filename>,
|
||||
<devicename>gm0s1e</devicename> for <filename>/usr</filename>,
|
||||
<devicename>gm0s1f</devicename> for
|
||||
<filename>/data1</filename>, and
|
||||
<devicename>gm0s1g</devicename> for
|
||||
<filename>/data2</filename>.</para>
|
||||
|
||||
<screen>&prompt.root; <userinput>gpart show mirror/gm0</userinput>
|
||||
=> 63 1953525104 mirror/gm0 MBR (931G)
|
||||
63 1953525042 1 freebsd [active] (931G)
|
||||
1953525105 62 - free - (31k)
|
||||
|
||||
&prompt.root; <userinput>gpart show mirror/gm0s1</userinput>
|
||||
=> 0 1953525042 mirror/gm0s1 BSD (931G)
|
||||
0 2097152 1 freebsd-ufs (1.0G)
|
||||
2097152 16777216 2 freebsd-swap (8.0G)
|
||||
18874368 41943040 4 freebsd-ufs (20G)
|
||||
60817408 20971520 5 freebsd-ufs (10G)
|
||||
81788928 629145600 6 freebsd-ufs (300G)
|
||||
710934528 1242590514 7 freebsd-ufs (592G)
|
||||
1953525042 63 - free - (31k)</screen>
|
||||
|
||||
<para>Both the slice and the last partition should have some
|
||||
free space at the end of each disk.</para>
|
||||
|
||||
<para>Create filesystems on these new partitions. The
|
||||
number of partitions will vary, matching the partitions on the
|
||||
original disk, <devicename>ada0</devicename>.</para>
|
||||
|
||||
<screen>&prompt.root; <userinput>newfs -U /dev/mirror/gm0s1a</userinput>
|
||||
&prompt.root; <userinput>newfs -U /dev/mirror/gm0s1d</userinput>
|
||||
&prompt.root; <userinput>newfs -U /dev/mirror/gm0s1e</userinput>
|
||||
&prompt.root; <userinput>newfs -U /dev/mirror/gm0s1f</userinput>
|
||||
&prompt.root; <userinput>newfs -U /dev/mirror/gm0s1g</userinput></screen>
|
||||
|
||||
<para>Make the mirror bootable by installing bootcode in the MBR
|
||||
and bsdlabel and setting the active slice:</para>
|
||||
|
||||
<screen>&prompt.root; <userinput>gpart bootcode -b /boot/mbr mirror/gm0</userinput>
|
||||
&prompt.root; <userinput>gpart set -a active -i 1 mirror/gm0</userinput>
|
||||
&prompt.root; <userinput>gpart bootcode -b /boot/boot mirror/gm0s1</userinput></screen>
|
||||
|
||||
<para>Adjust <filename>/etc/fstab</filename> to use the
|
||||
new partitions on the mirror. Back up this file first by
|
||||
copying it to <filename>/etc/fstab.orig</filename>.</para>
|
||||
|
||||
<screen>&prompt.root; <userinput>cp /etc/fstab /etc/fstab.orig</userinput></screen>
|
||||
|
||||
<para>Edit <filename>/etc/fstab</filename>, replacing
|
||||
<devicename>/dev/ada0</devicename> with
|
||||
<devicename>mirror/gm0</devicename>.</para>
|
||||
|
||||
<programlisting># Device Mountpoint FStype Options Dump Pass#
|
||||
/dev/mirror/gm0s1a / ufs rw 1 1
|
||||
/dev/mirror/gm0s1b none swap sw 0 0
|
||||
/dev/mirror/gm0s1d /var ufs rw 2 2
|
||||
/dev/mirror/gm0s1e /usr ufs rw 2 2
|
||||
/dev/mirror/gm0s1f /data1 ufs rw 2 2
|
||||
/dev/mirror/gm0s1g /data2 ufs rw 2 2</programlisting>
|
||||
|
||||
<para>If the &man.gmirror.8; kernel module has not been built
|
||||
into the kernel, edit <filename>/boot/loader.conf</filename>
|
||||
to load it:</para>
|
||||
|
||||
<programlisting>geom_mirror_load="YES"</programlisting>
|
||||
|
||||
<para>Filesystems from the original disk can now be copied onto
|
||||
the mirror with &man.dump.8; and &man.restore.8;. Note that
|
||||
it may take some time to create a snapshot for each filesystem
|
||||
dumped with <command>dump -L</command>.</para>
|
||||
|
||||
<screen>&prompt.root; <userinput>mount /dev/mirror/gm0s1a /mnt</userinput>
|
||||
&prompt.root; <userinput>dump -C16 -b64 -0aL -f - / | (cd /mnt && restore -rf -)</userinput>
|
||||
&prompt.root; <userinput>mount /dev/mirror/gm0s1d /mnt/var</userinput>
|
||||
&prompt.root; <userinput>mount /dev/mirror/gm0s1e /mnt/usr</userinput>
|
||||
&prompt.root; <userinput>mount /dev/mirror/gm0s1f /mnt/data1</userinput>
|
||||
&prompt.root; <userinput>mount /dev/mirror/gm0s1g /mnt/data2</userinput>
|
||||
&prompt.root; <userinput>dump -C16 -b64 -0aL -f - /usr | (cd /mnt/usr && restore -rf -)</userinput>
|
||||
&prompt.root; <userinput>dump -C16 -b64 -0aL -f - /var | (cd /mnt/var && restore -rf -)</userinput>
|
||||
&prompt.root; <userinput>dump -C16 -b64 -0aL -f - /data1 | (cd /mnt/data1 && restore -rf -)</userinput>
|
||||
&prompt.root; <userinput>dump -C16 -b64 -0aL -f - /data2 | (cd /mnt/data2 && restore -rf -)</userinput></screen>
|
||||
|
||||
<para>Restart the system, booting from
|
||||
<devicename>ada1</devicename>. If everything is working, the
|
||||
system will boot from <devicename>mirror/gm0</devicename>,
|
||||
which now contains the same data as
|
||||
<devicename>ada0</devicename> had previously. See the
|
||||
<link linkend="gmirror-troubleshooting">Troubleshooting</link>
|
||||
section if there are problems booting.</para>
|
||||
|
||||
<para>At this point, the mirror still consists of only the
|
||||
single <devicename>ada1</devicename> disk.</para>
|
||||
|
||||
<para>After booting from <devicename>mirror/gm0</devicename>
|
||||
successfully, the final step is inserting
|
||||
<devicename>ada0</devicename> into the mirror.</para>
|
||||
|
||||
<important>
|
||||
<para>When <devicename>ada0</devicename> is inserted into the
|
||||
mirror, its former contents will be overwritten by data on
|
||||
the mirror. Make certain that
|
||||
<devicename>mirror/gm0</devicename> has the same contents as
|
||||
<devicename>ada0</devicename> before adding
|
||||
<devicename>ada0</devicename> to the mirror. If there is
|
||||
something wrong with the contents copied by &man.dump.8; and
|
||||
&man.restore.8;, revert <filename>/etc/fstab</filename> to
|
||||
mount the filesystems on <devicename>ada0</devicename>,
|
||||
reboot, and try the whole procedure again.</para>
|
||||
</important>
|
||||
|
||||
<screen>&prompt.root; <userinput>gmirror insert gm0 ada0</userinput>
|
||||
GEOM_MIRROR: Device gm0: rebuilding provider ada0</screen>
|
||||
|
||||
<para>Synchronization between the two disks will start
|
||||
immediately. &man.gmirror.8; <command>status</command>
|
||||
shows the progress.</para>
|
||||
|
||||
<screen>&prompt.root; <userinput>gmirror status</userinput>
|
||||
Name Status Components
|
||||
mirror/gm0 DEGRADED ada1 (ACTIVE)
|
||||
ada0 (SYNCHRONIZING, 64%)</screen>
|
||||
|
||||
<para>After a while, synchronization will finish.</para>
|
||||
|
||||
<screen>GEOM_MIRROR: Device gm0: rebuilding provider ada0 finished.
|
||||
&prompt.root; <userinput>gmirror status</userinput>
|
||||
Name Status Components
|
||||
mirror/gm0 COMPLETE ada1 (ACTIVE)
|
||||
ada0 (ACTIVE)</screen>
|
||||
|
||||
<para><devicename>mirror/gm0</devicename> now consists of
|
||||
the two disks <devicename>ada0</devicename> and
|
||||
<devicename>ada1</devicename>, and the contents are
|
||||
automatically synchronized with each other. In use,
|
||||
<devicename>mirror/gm0</devicename> will behave just like the
|
||||
original single drive.</para>
|
||||
</sect2>
|
||||
|
||||
<sect2 id="gmirror-troubleshooting">
|
||||
<title>Troubleshooting</title>
|
||||
|
||||
<sect3>
|
||||
<title>System Refuses to Boot</title>
|
||||
<title>Problems with Booting</title>
|
||||
|
||||
<para>If the system boots up to a prompt similar to:</para>
|
||||
<sect4>
|
||||
<title>BIOS Settings</title>
|
||||
|
||||
<programlisting>ffs_mountroot: can't find rootvp
|
||||
Root mount failed: 6
|
||||
mountroot></programlisting>
|
||||
<para>BIOS settings may have to be changed to boot from one
|
||||
of the new mirrored drives. Either mirror drive can be
|
||||
used for booting. As components of a mirror, they contain
|
||||
identical data.</para>
|
||||
</sect4>
|
||||
|
||||
<para>Reboot the machine using the power or reset button. At
|
||||
the boot menu, select option six (6). This will drop the
|
||||
system to a &man.loader.8; prompt. Load the kernel module
|
||||
manually:</para>
|
||||
<sect4>
|
||||
<title>Boot Problems</title>
|
||||
|
||||
<screen>OK? <userinput>load geom_mirror</userinput>
|
||||
OK? <userinput>boot</userinput></screen>
|
||||
<para>If the boot stopped with this message, something is
|
||||
wrong with the mirror device:</para>
|
||||
|
||||
<para>If this works then for whatever reason the module was
|
||||
not being loaded properly. Check whether the relevant entry
|
||||
in <filename>/boot/loader.conf</filename> is correct. If
|
||||
the problem persists, place:</para>
|
||||
<screen>Mounting from ufs:/dev/mirror/gm0s1a failed with error 19.
|
||||
|
||||
<programlisting>options GEOM_MIRROR</programlisting>
|
||||
Loader variables:
|
||||
vfs.root.mountfrom=ufs:/dev/mirror/gm0s1a
|
||||
vfs.root.mountfrom.options=rw
|
||||
|
||||
<para>in the kernel configuration file, rebuild and reinstall.
|
||||
That should remedy this issue.</para>
|
||||
Manual root filesystem specification:
|
||||
<fstype>:<device> [options]
|
||||
Mount <device> using filesystem <fstype>
|
||||
and with the specified (optional) option list.
|
||||
|
||||
eg. ufs:/dev/da0s1a
|
||||
zfs:tank
|
||||
cd9660:/dev/acd0 ro
|
||||
(which is equivalent to: mount -t cd9660 -o ro /dev/acd0 /)
|
||||
|
||||
? List valid disk boot devices
|
||||
. Yield 1 second (for background tasks)
|
||||
<empty line> Abort manual input
|
||||
|
||||
mountroot></screen>
|
||||
|
||||
<para>Forgetting to load the
|
||||
<filename>geom_mirror</filename> module in
|
||||
<filename>/boot/loader.conf</filename> can cause this
|
||||
problem. To fix it, boot from a &os;-9 or later CD or USB
|
||||
stick and choose <literal>Shell</literal> at the first
|
||||
prompt. Then load the mirror module and mount the mirror
|
||||
device:</para>
|
||||
|
||||
<screen>&prompt.root; <userinput>gmirror load</userinput>
|
||||
&prompt.root; <userinput>mount /dev/mirror/gm0s1a /mnt</userinput></screen>
|
||||
|
||||
<para>Edit <filename>/mnt/boot/loader.conf</filename>,
|
||||
adding a line to load the mirror module:</para>
|
||||
|
||||
<programlisting>geom_mirror_load="YES"</programlisting>
|
||||
|
||||
<para>Save the file and reboot.</para>
|
||||
|
||||
<para>Other problems that cause <literal>error 19</literal>
|
||||
require more effort to fix. Enter
|
||||
<literal>ufs:/dev/ada0s1a</literal> at the prompt.
|
||||
Although the system should boot from
|
||||
<devicename>ada0</devicename>, another prompt to select a
|
||||
shell appears because <filename>/etc/fstab</filename> is
|
||||
incorrect. Press the Enter key at the prompt. Undo the
|
||||
modifications so far by reverting
|
||||
<filename>/etc/fstab</filename>, mounting filesystems from
|
||||
the original disk (<devicename>ada0</devicename>) instead
|
||||
of the mirror. Reboot the system and try the procedure
|
||||
again.</para>
|
||||
|
||||
<screen>Enter full pathname of shell or RETURN for /bin/sh:
|
||||
&prompt.root; <userinput>cp /etc/fstab.orig /etc/fstab</userinput>
|
||||
&prompt.root; <userinput>reboot</userinput></screen>
|
||||
</sect4>
|
||||
</sect3>
|
||||
</sect2>
|
||||
|
||||
<sect2>
|
||||
<title>Recovering from Disk Failure</title>
|
||||
|
||||
<para>The wonderful part about disk mirroring is that when a
|
||||
disk fails, it may be replaced, presumably, without losing
|
||||
<para>The wonderful part about disk mirroring is that an
|
||||
individual disk can fail without causing the mirror to lose
|
||||
any data.</para>
|
||||
|
||||
<para>Considering the previous <acronym>RAID</acronym>1
|
||||
configuration, assume that <devicename>da1</devicename>
|
||||
has failed and now needs to be replaced. To replace it,
|
||||
determine which disk has failed and power down the system.
|
||||
At this point, the disk may be swapped with a new one and
|
||||
the system brought back up. After the system has restarted,
|
||||
the following commands may be used to replace the disk:</para>
|
||||
<para><devicename>ada0</devicename> is one of two drives making
|
||||
up the mirror in the previous example. If
|
||||
<devicename>ada0</devicename> fails, the mirror will continue
|
||||
to work, providing data from the remaining working drive,
|
||||
<devicename>ada1</devicename>.</para>
|
||||
|
||||
<para>To replace the failed drive, the computer is shut down and
|
||||
the failed drive is physically replaced with a new drive of
|
||||
equal or greater capacity. Manufacturers use somewhat
|
||||
arbitrary values when rating drives in gigabytes, and the
|
||||
only way to really be sure is to compare the total count of
|
||||
sectors shown by <command>diskinfo -v</command>. A drive with
|
||||
larger capacity than the mirror will work, although the extra
|
||||
space on the new drive will not be used.</para>
|
||||
|
||||
<para>After the computer is powered back up, the mirror will be
|
||||
running in a <quote>degraded</quote> mode with only one drive.
|
||||
The mirror is told to forget drives that are not currently
|
||||
connected:</para>
|
||||
|
||||
<screen>&prompt.root; <userinput>gmirror forget gm0</userinput></screen>
|
||||
|
||||
<screen>&prompt.root; <userinput>gmirror insert gm0 /dev/da1</userinput></screen>
|
||||
<para>Any old metadata should be <link
|
||||
linkend="GEOM-mirror-metadata">cleared from the replacement
|
||||
disk</link>. Then the disk, <devicename>ada4</devicename>
|
||||
for this example, is inserted into the mirror:</para>
|
||||
|
||||
<para>Use the <command>gmirror</command> <option>status</option>
|
||||
command to monitor the progress of the rebuild. It is that
|
||||
simple.</para>
|
||||
<screen>&prompt.root; <userinput>gmirror insert gm0 /dev/ada4</userinput></screen>
|
||||
|
||||
<para>Resynchronization begins when the new drive is inserted
|
||||
into the mirror. This process of copying mirror data to a new
|
||||
drive can take a while. Performance of the mirror will be
|
||||
greatly reduced during the copy, so inserting new drives is
|
||||
best done when there is low demand on the computer.</para>
|
||||
|
||||
<para>Progress can be monitored with <command>gmirror
|
||||
status</command>, which shows drives that are being
|
||||
synchronized and the percentage of completion. During
|
||||
resynchronization, the status will be
|
||||
<computeroutput>DEGRADED</computeroutput>, changing to
|
||||
<computeroutput>COMPLETE</computeroutput> when the process is
|
||||
finished.</para>
|
||||
</sect2>
|
||||
</sect1>
|
||||
|
||||
|
|
@ -489,7 +877,7 @@ OK? <userinput>boot</userinput></screen>
|
|||
fault tolerance of 1 drive, while providing a capacity of 1 - 1/n
|
||||
times the total capacity of all drives in the array, where n is the
|
||||
number of hard drives in the array. Such a configuration is
|
||||
mostly suitable for storing data of larger sizes, e.g.
|
||||
mostly suitable for storing data of larger sizes, e.g.,
|
||||
multimedia files.</para>
|
||||
|
||||
<para>At least 3 physical hard drives are required to build a
|
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|
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Reference in a new issue