Significant cleanup/rewrite of GEOM Striping section.
* This chapter claims to be about striping, but talks about disk concatenation in some paragraphs. Remove all references to concatenation, add a brief paragraph explaining what striping is and why it provides superior I/O performance through parallel I/O to multiple disks simultaneously. * Do not alternate between calling striping raid0 and raid1. Consistently refer to it as raid0, as raid1 is mirroring. * Cleanup / reorganize the example set of commands for creating a stripe of two ATA disks. Wrap it in a DocBook <procedure> tag with individual <steps> to provide a title for this procedure and make the numbered steps very clear to follow without confusing verbiage and side tangents adding confusion. * Expand 'redundant array of inexpensive disks' in <acronym> tag for mouseover on first use of HTML output. * Remove some poorly worded, confusing, and contradictory sentences and paragraphs.
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Murray Stokely
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2020-12-08 03:00:23 +00:00
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1 changed files with 98 additions and 65 deletions
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@ -29,16 +29,16 @@
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</indexterm>
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<para>This chapter covers the use of disks under the new GEOM
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framework in &os;. This includes the major
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<acronym>RAID</acronym> control utilities which use the
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framework for configuration. This chapter will not go
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into in depth discussion on how GEOM handles or controls
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I/O, the underlying subsystem, or code. This information
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is provided through the &man.geom.4; manual page and its various
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SEE ALSO references. This chapter is also not a definitive guide
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to <acronym>RAID</acronym> configurations. Only GEOM
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supported <acronym>RAID</acronym> classifications will be
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discussed.</para>
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framework in &os;. This includes the major <acronym
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role="Redundant Array of Inexpensive Disks">RAID</acronym>
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control utilities which use the framework for configuration.
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This chapter will not go into in depth discussion on how GEOM
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handles or controls I/O, the underlying subsystem, or code.
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This information is provided through the &man.geom.4; manual
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page and its various SEE ALSO references. This chapter is also
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not a definitive guide to <acronym>RAID</acronym>
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configurations. Only GEOM supported <acronym>RAID</acronym>
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classifications will be discussed.</para>
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<para>After reading this chapter, you will know:</para>
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@ -91,6 +91,20 @@
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</sect1>
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<sect1 id="GEOM-striping">
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<sect1info>
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<authorgroup>
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<author>
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<firstname>Tom</firstname>
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<surname>Rhodes</surname>
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<contrib>Written by </contrib>
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</author>
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<author>
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<firstname>Murray</firstname>
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<surname>Stokely</surname>
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</author>
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</authorgroup>
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</sect1info>
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<title>RAID0 - Striping</title>
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<indexterm>
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@ -102,84 +116,103 @@
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<para>Striping is a method used to combine several disk drives into
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a single volume. In many cases, this is done through the use of
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hardware controllers supporting all variants of disks,
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<acronym>SCSI</acronym>, <acronym>SATA</acronym>,
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and <acronym>ATA</acronym>. The GEOM disk subsystem provides
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software support for <acronym>RAID</acronym>1, also known as
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hardware controllers. The GEOM disk subsystem provides
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software support for <acronym>RAID</acronym>0, also known as
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disk striping.</para>
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<para>Some cases have this volume, comprised of several disks, as a
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separate file system for backups, data storage for users;
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however, in other cases still, this volume may hold the root, or
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<filename role="directory">/</filename> partition and the system
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will boot from it. Both will be described herein.</para>
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<para>In a <acronym>RAID</acronym>0 system, data are split up in
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blocks that get written across all the drives in the array.
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Instead of having to wait on the system to write 256k to one
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disk, a <acronym>RAID</acronym>0 system can simultaneously write
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64k to each of four different disks, offering superior I/O
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performance. This performance can be enhanced further by using
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multiple disk controllers.</para>
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<para>To stripe several <acronym>ATA</acronym> disks, of the same
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size of course, load the <filename>geom_stripe</filename>
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module:</para>
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<para>Each disk in a <acronym>RAID</acronym>0 stripe must be of
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the same size, since I/O requests are interleaved to read or
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write to multiple disks in parallel.</para>
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<procedure>
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<title>Creating a stripe of unformatted ATA disks</title>
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<step><para>Load the <filename>geom_stripe</filename>
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module:</para>
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<screen>&prompt.root; <userinput>kldload geom_stripe.ko</userinput></screen>
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</step>
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<para>The module should now be loaded and visible from the output of
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<command>kldstat</command>. Now to combine the disks. Ensure
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that a mount point exists, if this volume will become a root
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partition then temporarily use
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<filename role="directory">/mnt</filename>. Otherwise, for the
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purpose of our examples, this volume will reside at the
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<filename role="directory">/home</filename> mount point. This
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process may be complicated if users already exist on the system.
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If so, assume the volume will reside on
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<filename role="directory">/data</filename>.</para>
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<step><para>Ensure that a suitable mount point exists. If this
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volume will become a root partition, then temporarily use
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another mount point such as <filename
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role="directory">/mnt</filename>.</para>
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<para>Begin by selecting the disks which will be striped. Our
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scenario has two unused, unpartitioned <acronym>ATA</acronym>
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disks: <filename>/dev/ad2</filename> and
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<filename>/dev/ad3</filename>. The module has been loaded and
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our disks selected, we will now create the stripe device:</para>
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<screen>&prompt.root; <userinput>mkdir /mnt</userinput></screen>
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</step>
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<screen>&prompt.root; <userinput>gstripe label -v st0 /dev/ad2 /dev/ad3</userinput></screen>
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<step><para>Determine the device names for the disks which will
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be striped, and create the new stripe device. For example,
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the following command could be used to stripe two unused,
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unpartitioned <acronym>ATA</acronym> disks:
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<filename>/dev/ad2</filename> and
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<filename>/dev/ad3</filename>.</para>
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<screen>&prompt.root; <userinput>gstripe label -v st0 /dev/ad2 /dev/ad3</userinput></screen>
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<!--
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<para>A message should be returned explaining that meta data has
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been stored on the devices. The file system must now be created
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on the device. If this volume is to be used for system
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initialization, the following command must be issued before the
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file system is created:</para>
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been stored on the devices.
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XXX: What message? Put it inside the screen output above.
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-->
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</step>
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<screen>&prompt.root; <userinput>fdisk -vBI /dev/stripe/st0</userinput></screen>
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<step><para>If this volume will be used as a root device for
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booting the system, then the following command must be issued
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before the file system is created:</para>
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<para>Create a partition table on the new volume:</para>
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<screen>&prompt.root; <userinput>fdisk -vBI /dev/stripe/st0</userinput></screen>
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</step>
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<screen>&prompt.root; <userinput>bsdlabel -wB /dev/stripe/st0</userinput></screen>
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<step><para>A partition table must be created on the new volume
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with the following command:</para>
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<para>This process should have created two other devices in the
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<filename role="directory">/dev/stripe</filename> directory in
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addition to the <filename>st0</filename> device. Those include
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<filename>st0a</filename> and <filename>st0c</filename>. Next a
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file system must be created on the device using
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<command>newfs</command>:</para>
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<screen>&prompt.root; <userinput>bsdlabel -wB /dev/stripe/st0</userinput></screen>
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<screen>&prompt.root; <userinput>newfs -U /dev/stripe/st0a</userinput></screen>
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</step>
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<para>Many numbers will glide across the screen, and after a few
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seconds, the process will be complete. The volume has been
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created and is ready to be hung from its <command>mount</command>
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point:</para>
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<step><para>This process should have created two other devices
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in the <filename role="directory">/dev/stripe</filename>
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directory in addition to the <filename>st0</filename> device.
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Those include <filename>st0a</filename> and
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<filename>st0c</filename>. A file system must now be created
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on the <filename>st0a</filename> device using the following
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<command>newfs</command> command:</para>
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<screen>&prompt.root; <userinput>mount /dev/stripe/st0a /home</userinput></screen>
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<screen>&prompt.root; <userinput>newfs -U /dev/stripe/st0a</userinput></screen>
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<para>Place the volume information in
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<filename>/etc/fstab</filename> file:</para>
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<para>Many numbers will glide across the screen, and after a few
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seconds, the process will be complete. The volume has been
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created and is ready to be mounted:</para>
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</step>
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</procedure>
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<screen>&prompt.root; <userinput>echo "/dev/stripe/st0a /home ufs rw 2 2" \</userinput>
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<para>The following command can be used to manually mount a newly
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created disk stripe.</para>
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<screen>&prompt.root; <userinput>mount /dev/stripe/st0a /mnt</userinput></screen>
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<para>To mount this striped filesystem automatically during the boot
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process, place the volume information in
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<filename>/etc/fstab</filename> file:</para>
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<screen>&prompt.root; <userinput>echo "/dev/stripe/st0a /mnt ufs rw 2 2" \</userinput>
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<userinput>>> /etc/fstab</userinput></screen>
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<para>And load the module during system initialization:</para>
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<para>The geom module must also be automatically loaded during
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system initialization, by adding a line to
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<filename>/boot/loader.conf</filename>.</para>
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<screen>&prompt.root; <userinput>echo 'geom_stripe_load="YES"' >> /boot/loader.conf</userinput></screen>
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<screen>&prompt.root; <userinput>echo 'geom_stripe_load="YES"' >> /boot/loader.conf</userinput></screen>
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<para>From here on, all users will have their data stored on the
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striped volume comprised of the disks concatenated in the
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beginning.</para>
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</sect1>
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<sect1 id="GEOM-mirror">
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