Date: Tue, 31 Jan 2012 13:58:44 -0700 (MST) From: Warren Block <wblock@wonkity.com> To: Daniel Gerzo <danger@freebsd.org> Cc: doc@freebsd.org Subject: Re: New Handbook Section for Review - graid3 Message-ID: <alpine.BSF.2.00.1201311344400.97077@wonkity.com> In-Reply-To: <20120131104953.GA55314@freefall.freebsd.org> References: <20120131104953.GA55314@freefall.freebsd.org>
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[-- Attachment #1 --] On Tue, 31 Jan 2012, Daniel Gerzo wrote: > A new Handbook section covering graid3 is now available for review; > the patch is attached. > > The text is based on PR 164228. A built version is available at > http://people.freebsd.org/~danger/geom-raid3.html. > > Comments are welcome. Patch with suggested changes attached. This is a full diff, not a diff to your diff. Some general things I'm not sure about, but will suggest: Personally, I prefer add this setting to configfile <programlisting>'blahblah'</programlisting> to Run this command <screen>'echo blahblah >> configfile'</screen> I did not change those, though. Various wording changes. The sentence explaining total capacity could still be better, I think. Paragraphs were intentionally not rewrapped, but should be. The paragraph starting "To retain this configuration across reboots" was unclear. I hope it still means what it did. A couple of blank lines had whitespace. Title capitalization was changed a bit. igor (http://www.wonkity.com/~wblock/igor/) can proofread those. [-- Attachment #2 --] Index: chapter.sgml =================================================================== RCS file: /home/dcvs/doc/en_US.ISO8859-1/books/handbook/geom/chapter.sgml,v retrieving revision 1.51 diff -u -r1.51 chapter.sgml --- chapter.sgml 21 Nov 2011 18:11:25 -0000 1.51 +++ chapter.sgml 31 Jan 2012 20:44:15 -0000 @@ -436,6 +436,162 @@ </sect2> </sect1> + <sect1 id="GEOM-raid3"> + <sect1info> + <authorgroup> + <author> + <firstname>Mark</firstname> + <surname>Gladman</surname> + <contrib>Written by </contrib> + </author> + <author> + <firstname>Daniel</firstname> + <surname>Gerzo</surname> + </author> + </authorgroup> + <authorgroup> + <author> + <firstname>Tom</firstname> + <surname>Rhodes</surname> + <contrib>Based on documentation by </contrib> + </author> + <author> + <firstname>Murray</firstname> + <surname>Stokely</surname> + </author> + </authorgroup> + </sect1info> + + <indexterm> + <primary>GEOM</primary> + </indexterm> + <indexterm> + <primary>RAID3</primary> + </indexterm> + + <title><acronym>RAID</acronym>3 - Byte-level Striping with Dedicated + Parity</title> + + <para><acronym>RAID</acronym>3 is a method used to combine several + disk drives into a single volume with a dedicated parity + disk. In a <acronym>RAID</acronym>3 system, data is split up + into a number of bytes that get written across all the drives in + the array except for one disk which acts as a dedicated parity + disk. This means that reading 1024KB from a + <acronym>RAID</acronym>3 implementation will access all disks in + the array. Performance can be enhanced by using multiple + disk controllers. The <acronym>RAID</acronym>3 array provides a + 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. + multimedia files.</para> + + <para>At least 3 physical hard drives are required to build a + <acronym>RAID</acronym>3 array. Each disk must be of the same + size, since I/O requests are interleaved to read or write to + multiple disks in parallel. Also due to the nature of + <acronym>RAID</acronym>3, the number of drives must be + equal to 3, 5, 9, 17, etc. (2^n + 1).</para> + + <sect2> + <title>Creating a Dedicated <acronym>RAID</acronym>3 Array</title> + + <para>In &os;, support for <acronym>RAID</acronym>3 is + implemented by the &man.graid3.8; <acronym>GEOM</acronym> + class. Creating a dedicated + <acronym>RAID</acronym>3 array on &os; requires the following steps.</para> + + <note> + <para>While it is theoretically possible to boot from a + <acronym>RAID</acronym>3 array on &os;, such a configuration + is not common and is not advised. As such, this section + does not describe how to accomplish that + configuration.</para> + </note> + + <procedure> + <step> + <para>First, load the <filename>geom_raid3.ko</filename> kernel module.</para> + + <screen>&prompt.root; <userinput>graid3 load</userinput></screen> + + <para>Alternatively, it is possible to manually load the + <filename>geom_raid3.ko</filename> module:</para> + + <screen>&prompt.root; <userinput>kldload geom_raid3.ko</userinput></screen> + </step> + + <step> + <para>Create or ensure that a suitable mount point + exists:</para> + + <screen>&prompt.root; <userinput>mkdir <replaceable>/multimedia/</replaceable></userinput></screen> + </step> + + <step> + <para>Determine the device names for the disks which will be + added to the array, and create the new + <acronym>RAID</acronym>3 device. The final device listed + will act as the dedicated parity disk. This + example uses three unpartitioned + <acronym>ATA</acronym> drives: + <devicename><replaceable>ada1</replaceable></devicename> + and <devicename><replaceable>ada2</replaceable></devicename> + for data, and + <devicename><replaceable>ada3</replaceable></devicename> + for parity.</para> + + <screen>&prompt.root; <userinput>graid3 label -v gr0 /dev/ada1 /dev/ada2 /dev/ada3</userinput> +Metadata value stored on /dev/ada1. +Metadata value stored on /dev/ada2. +Metadata value stored on /dev/ada3. +Done.</screen> + </step> + + <step> + <para>Partition the newly created + <devicename>gr0</devicename> device and put a UFS file + system on it:</para> + + <screen>&prompt.root; <userinput>gpart create -s GPT /dev/raid3/gr0</userinput> +&prompt.root; <userinput>gpart add -t freebsd-ufs /dev/raid3/gr0</userinput> +&prompt.root; <userinput>newfs -j /dev/raid3/gr0p1</userinput></screen> + + <para>Many numbers will glide across the screen, and after a + few seconds, the process will be complete. The volume has + been created and is ready to be mounted.</para> + </step> + + <step> + <para>The last step is to mount the file system:</para> + + <screen>&prompt.root; <userinput>mount /dev/raid3/gr0p1 /multimedia/</userinput></screen> + + <para>The <acronym>RAID</acronym>3 array is now ready to + use.</para> + </step> + </procedure> + + <note> + <para>The + <filename>geom_raid3.ko</filename> module must be loaded + before the array can be mounted. To + automatically load the kernel module during system initialization, + invoke the following command:</para> + + <screen>&prompt.root; <userinput>echo 'geom_raid3_load="YES"' >> /boot/loader.conf</userinput></screen> + + <para>For + automatic mounting of the array's file system during the boot + process, add the volume information in + <filename>/etc/fstab</filename> file:</para> + + <screen>&prompt.root; <userinput>echo "/dev/raid3/gr0p1 /multimedia ufs rw 2 2" >> /etc/fstab</userinput></screen> + </note> + </sect2> + </sect1> + <sect1 id="geom-ggate"> <title>GEOM Gate Network Devices</title>help
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