svn commit: r42527 - head/en_US.ISO8859-1/books/handbook/geom
Warren Block
wblock at FreeBSD.org
Sat Aug 10 18:25:26 UTC 2013
Author: wblock
Date: Sat Aug 10 18:25:25 2013
New Revision: 42527
URL: http://svnweb.freebsd.org/changeset/doc/42527
Log:
Add a new section on graid(8). Many people helped with review and
corrections, including Allan Jude, bjk, brd, and mav.
Modified:
head/en_US.ISO8859-1/books/handbook/geom/chapter.xml
Modified: head/en_US.ISO8859-1/books/handbook/geom/chapter.xml
==============================================================================
--- head/en_US.ISO8859-1/books/handbook/geom/chapter.xml Fri Aug 9 21:49:13 2013 (r42526)
+++ head/en_US.ISO8859-1/books/handbook/geom/chapter.xml Sat Aug 10 18:25:25 2013 (r42527)
@@ -824,6 +824,314 @@ mountroot></screen>
</sect2>
</sect1>
+ <sect1 id="geom-graid">
+ <sect1info>
+ <authorgroup>
+ <author>
+ <firstname>Warren</firstname>
+ <surname>Block</surname>
+ <contrib>Originally contributed by </contrib>
+ </author>
+ </authorgroup>
+ </sect1info>
+ <title>Software <acronym>RAID</acronym> Devices</title>
+
+ <indexterm>
+ <primary>GEOM</primary>
+ </indexterm>
+ <indexterm>
+ <primary>Software RAID Devices</primary>
+ <secondary>Hardware-assisted RAID</secondary>
+ </indexterm>
+
+ <para>Some motherboards and expansion cards add some simple
+ hardware, usually just a <acronym>ROM</acronym>, that allows the
+ computer to boot from a <acronym>RAID</acronym> array. After
+ booting, access to the <acronym>RAID</acronym> array is handled
+ by software running on the computer's main processor. This
+ <quote>hardware-assisted software
+ <acronym>RAID</acronym></quote> gives <acronym>RAID</acronym>
+ arrays that are not dependent on any particular operating
+ system, and which are functional even before an operating system
+ is loaded.</para>
+
+ <para>Several levels of <acronym>RAID</acronym> are supported,
+ depending on the hardware in use. See &man.graid.8; for a
+ complete list.</para>
+
+ <para>&man.graid.8; requires the <filename>geom_raid.ko</filename>
+ kernel module, which is included in the
+ <filename>GENERIC</filename> kernel starting with &os; 9.1.
+ If needed, it can be loaded manually with
+ <command>graid load</command>.</para>
+
+ <sect2 id="geom-graid-creating">
+ <title>Creating an Array</title>
+
+ <para>Software <acronym>RAID</acronym> devices often have a menu
+ that can be entered by pressing special keys when the computer
+ is booting. The menu can be used to create and delete
+ <acronym>RAID</acronym> arrays. &man.graid.8; can also create
+ arrays directly from the command line.</para>
+
+ <para><command>graid label</command> is used to create a new
+ array. The motherboard used for this example has an Intel
+ software <acronym>RAID</acronym> chipset, so the Intel
+ metadata format is specified. The new array is given a label
+ of <devicename>gm0</devicename>, it is a mirror
+ (<acronym>RAID1</acronym>), and uses drives
+ <devicename>ada0</devicename> and
+ <devicename>ada1</devicename>.</para>
+
+ <caution>
+ <para>Some space on the drives will be overwritten when they
+ are made into a new array. Back up existing data
+ first!</para>
+ </caution>
+
+ <screen>&prompt.root; <userinput>graid label Intel gm0 RAID1 ada0 ada1</userinput>
+GEOM_RAID: Intel-a29ea104: Array Intel-a29ea104 created.
+GEOM_RAID: Intel-a29ea104: Disk ada0 state changed from NONE to ACTIVE.
+GEOM_RAID: Intel-a29ea104: Subdisk gm0:0-ada0 state changed from NONE to ACTIVE.
+GEOM_RAID: Intel-a29ea104: Disk ada1 state changed from NONE to ACTIVE.
+GEOM_RAID: Intel-a29ea104: Subdisk gm0:1-ada1 state changed from NONE to ACTIVE.
+GEOM_RAID: Intel-a29ea104: Array started.
+GEOM_RAID: Intel-a29ea104: Volume gm0 state changed from STARTING to OPTIMAL.
+Intel-a29ea104 created
+GEOM_RAID: Intel-a29ea104: Provider raid/r0 for volume gm0 created.</screen>
+
+ <para>A status check shows the new mirror is ready for
+ use:</para>
+
+ <screen>&prompt.root; <userinput>graid status</userinput>
+ Name Status Components
+raid/r0 OPTIMAL ada0 (ACTIVE (ACTIVE))
+ ada1 (ACTIVE (ACTIVE))</screen>
+
+ <para>The array device appears in
+ <filename>/dev/raid/</filename>. The first array is called
+ <devicename>r0</devicename>. Additional arrays, if present,
+ will be <devicename>r1</devicename>,
+ <devicename>r2</devicename>, and so on.</para>
+
+ <para>The <acronym>BIOS</acronym> menu on some of these devices
+ can create arrays with special characters in their names. To
+ avoid problems with those special characters, arrays are given
+ simple numbered names like <devicename>r0</devicename>. To
+ show the actual labels, like <devicename>gm0</devicename> in
+ the example above, use &man.sysctl.8;:</para>
+
+ <screen>&prompt.root; <userinput>sysctl kern.geom.raid.name_format=1</userinput></screen>
+ </sect2>
+
+ <sect2 id="geom-graid-volumes">
+ <title>Multiple Volumes</title>
+
+ <para>Some software <acronym>RAID</acronym> devices support
+ more than one <emphasis>volume</emphasis> on an array.
+ Volumes work like partitions, allowing space on the physical
+ drives to be split and used in different ways. For example,
+ Intel software <acronym>RAID</acronym> devices support two
+ volumes. This example creates a 40 G mirror for safely
+ storing the operating system, followed by a 20 G
+ <acronym>RAID0</acronym> (stripe) volume for fast temporary
+ storage:</para>
+
+ <screen>&prompt.root; <userinput>graid label -S 40G Intel gm0 RAID1 ada0 ada1</userinput>
+&prompt.root; <userinput>graid add -S 20G gm0 RAID0</userinput></screen>
+
+ <para>Volumes appear as additional
+ <devicename>r<replaceable>X</replaceable></devicename> entries
+ in <filename>/dev/raid/</filename>. An array with two volumes
+ will show <devicename>r0</devicename> and
+ <devicename>r1</devicename>.</para>
+
+ <para>See &man.graid.8; for the number of volumes supported by
+ different software <acronym>RAID</acronym> devices.</para>
+ </sect2>
+
+ <sect2 id="geom-graid-converting">
+ <title>Converting a Single Drive to a Mirror</title>
+
+ <para>Under certain specific conditions, it is possible to
+ convert an existing single drive to a &man.graid.8; array
+ without reformatting. To avoid data loss during the
+ conversion, the existing drive must meet these minimum
+ requirements:</para>
+
+ <itemizedlist>
+ <listitem>
+ <para>The drive must be partitioned with the
+ <acronym>MBR</acronym> partitioning scheme.
+ <acronym>GPT</acronym> or other partitioning schemes with
+ metadata at the end of the drive will be overwritten and
+ corrupted by the &man.graid.8; metadata.</para>
+ </listitem>
+
+ <listitem>
+ <para>There must be enough unpartitioned and unused space at
+ the end of the drive to hold the &man.graid.8; metadata.
+ This metadata varies in size, but the largest occupies
+ 64 M, so at least that much free space is
+ recommended.</para>
+ </listitem>
+ </itemizedlist>
+
+ <para>If the drive meets these requirements, start by making a
+ full backup. Then create a single-drive mirror with that
+ drive:</para>
+
+ <screen>&prompt.root; <userinput>graid label Intel gm0 RAID1 ada0 NONE</userinput></screen>
+
+ <para>&man.graid.8; metadata was written to the end of the drive
+ in the unused space. A second drive can now be inserted into
+ the mirror:</para>
+
+ <screen>&prompt.root; <userinput>graid insert raid/r0 ada1</userinput></screen>
+
+ <para>Data from the original drive will immediately begin to be
+ copied to the second drive. The mirror will operate in
+ degraded status until the copy is complete.</para>
+ </sect2>
+
+ <sect2 id="geom-graid-inserting">
+ <title>Inserting New Drives into the Array</title>
+
+ <para>Drives can be inserted into an array as replacements for
+ drives that have failed or are missing. If there are no
+ failed or missing drives, the new drive becomes a spare. For
+ example, inserting a new drive into a working two-drive mirror
+ results in a two-drive mirror with one spare drive, not a
+ three-drive mirror.</para>
+
+ <para>In the example mirror array, data immediately begins to be
+ copied to the newly-inserted drive. Any existing information
+ on the new drive will be overwritten.</para>
+
+ <screen>&prompt.root; <userinput>graid insert raid/r0 ada1</userinput>
+GEOM_RAID: Intel-a29ea104: Disk ada1 state changed from NONE to ACTIVE.
+GEOM_RAID: Intel-a29ea104: Subdisk gm0:1-ada1 state changed from NONE to NEW.
+GEOM_RAID: Intel-a29ea104: Subdisk gm0:1-ada1 state changed from NEW to REBUILD.
+GEOM_RAID: Intel-a29ea104: Subdisk gm0:1-ada1 rebuild start at 0.</screen>
+ </sect2>
+
+ <sect2 id="geom-graid-removing">
+ <title>Removing Drives from the Array</title>
+
+ <para>Individual drives can be permanently removed from a
+ from an array and their metadata erased:</para>
+
+ <screen>&prompt.root; <userinput>graid remove raid/r0 ada1</userinput>
+GEOM_RAID: Intel-a29ea104: Disk ada1 state changed from ACTIVE to OFFLINE.
+GEOM_RAID: Intel-a29ea104: Subdisk gm0:1-[unknown] state changed from ACTIVE to NONE.
+GEOM_RAID: Intel-a29ea104: Volume gm0 state changed from OPTIMAL to DEGRADED.</screen>
+ </sect2>
+
+ <sect2 id="geom-graid-stopping">
+ <title>Stopping the Array</title>
+
+ <para>An array can be stopped without removing metadata from the
+ drives. The array will be restarted when the system is
+ booted.</para>
+
+ <screen>&prompt.root; <userinput>graid stop raid/r0</userinput></screen>
+ </sect2>
+
+ <sect2 id="geom-graid-status">
+ <title>Checking Array Status</title>
+
+ <para>Array status can be checked at any time. After a drive
+ was added to the mirror in the example above, data is being
+ copied from the original drive to the new drive:</para>
+
+ <screen>&prompt.root; <userinput>graid status</userinput>
+ Name Status Components
+raid/r0 DEGRADED ada0 (ACTIVE (ACTIVE))
+ ada1 (ACTIVE (REBUILD 28%))</screen>
+
+ <para>Some types of arrays, like <literal>RAID0</literal> or
+ <literal>CONCAT</literal>, may not be shown in the status
+ report if disks have failed. To see these partially-failed
+ arrays, add <option>-ga</option>:</para>
+
+ <screen>&prompt.root; <userinput>graid status -ga</userinput>
+ Name Status Components
+Intel-e2d07d9a BROKEN ada6 (ACTIVE (ACTIVE))</screen>
+ </sect2>
+
+ <sect2 id="geom-graid-deleting">
+ <title>Deleting Arrays</title>
+
+ <para>Arrays are destroyed by deleting all of the volumes from
+ them. When the last volume present is deleted, the array is
+ stopped and metadata is removed from the drives:</para>
+
+ <screen>&prompt.root; <userinput>graid delete raid/r0</userinput></screen>
+ </sect2>
+
+ <sect2 id="geom-graid-unexpected">
+ <title>Deleting Unexpected Arrays</title>
+
+ <para>Drives may unexpectedly contain &man.graid.8; metadata,
+ either from previous use or manufacturer testing.
+ &man.graid.8; will detect these drives and create an array,
+ interfering with access to the individual drive. To remove
+ the unwanted metadata:</para>
+
+ <procedure>
+ <step>
+ <para>Boot the system. At the boot menu, select
+ <literal>2</literal> for the loader prompt. Enter:</para>
+
+ <screen>OK <userinput>set kern.geom.raid.enable=0</userinput>
+OK <userinput>boot</userinput></screen>
+
+ <para>The system will boot with &man.graid.8;
+ disabled.</para>
+ </step>
+
+ <step>
+ <para>Back up all data on the affected drive.</para>
+ </step>
+
+ <step>
+ <para>As a workaround, &man.graid.8; array detection
+ can be disabled by adding</para>
+
+ <programlisting>kern.geom.raid.enable=0</programlisting>
+
+ <para>to <filename>/boot/loader.conf</filename>.</para>
+
+ <para>To permanently remove the &man.graid.8; metadata
+ from the affected drive, boot a &os; installation
+ <acronym>CD-ROM</acronym> or memory stick, and select
+ <literal>Shell</literal>. Use <command>status</command>
+ to find the name of the array, typically
+ <literal>raid/r0</literal>:</para>
+
+ <screen>&prompt.root; <userinput>graid status</userinput>
+ Name Status Components
+raid/r0 OPTIMAL ada0 (ACTIVE (ACTIVE))
+ ada1 (ACTIVE (ACTIVE))</screen>
+
+ <para>Delete the volume by name:</para>
+
+ <screen>&prompt.root; <userinput>graid delete raid/r0</userinput></screen>
+
+ <para>If there is more than one volume shown, repeat the
+ process for each volume. After the last array has been
+ deleted, the volume will be destroyed.</para>
+
+ <para>Reboot and verify data, restoring from backup if
+ necessary. After the metadata has been removed, the
+ <literal>kern.geom.raid.enable=0</literal> entry in
+ <filename>/boot/loader.conf</filename> can also be
+ removed.</para>
+ </step>
+ </procedure>
+ </sect2>
+ </sect1>
+
<sect1 id="geom-raid3">
<sect1info>
<authorgroup>
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