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git-svn-id: svn://svn.linuxfromscratch.org/BLFS/trunk/BOOK@11015 af4574ff-66df-0310-9fd7-8a98e5e911e0
112 lines
4.3 KiB
XML
112 lines
4.3 KiB
XML
<?xml version="1.0" encoding="ISO-8859-1"?>
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<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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<!ENTITY % general-entities SYSTEM "../../general.ent">
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%general-entities;
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]>
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<sect1 id="aboutlvm">
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<?dbhtml filename="aboutlvm.html"?>
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<sect1info>
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<othername>$LastChangedBy$</othername>
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<date>$Date$</date>
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</sect1info>
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<title>About Logical Volume Management (LVM)</title>
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<para>LVM manages disk drives. It allows multiple drives and partitions
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to be combined into larger <emphasis>volume groups</emphasis>, assists in
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making backups through a <emphasis>snapshot</emphasis>, and allows for
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dynamic volume resizing. It can also provide mirroring similar to
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a RAID 1 array.</para>
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<para>A complete discussion of LVM is beyond the scope of this introduction,
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but basic concepts are presented below.</para>
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<para>To run any of the commands presented here, the <xref linkend='lvm2'/>
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package must be installed. All commands must be run as the <systemitem
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class="username">root</systemitem> user.</para>
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<para>Management of disks with lvm is accomplished using the following
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concepts: </para>
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<variablelist>
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<varlistentry>
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<term>physical volumes</term>
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<listitem><para>These are physical disks or partitions such as
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/dev/sda3 or /dev/sdb.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>volume groups</term>
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<listitem><para>These are named groups of physical volumes that
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can be manipulated by the administrator. The number of physical
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volumes that make up a volume group is arbitrary. Physical volumes
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can be dynamically added or removed from a volume group.
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</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>logical volumes</term>
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<listitem><para>Volume groups may be subdivided into logical volumes.
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Each logical volume can then be individually formatted as if it were a
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regular Linux partition. Logical volumes may be dynamically resized by
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the administrator according to need.</para></listitem>
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</varlistentry>
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</variablelist>
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<para>To give a concrete example, suppose that you have two 2 TB disks.
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Also suppose a really large amount of space is required for a very large database,
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mounted on <filename class='directory'>/srv/mysql</filename>. This is what
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the initial set of partitions would look like:</para>
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<screen><literal>Partition Use Size Partition Type
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/dev/sda1 /boot 100MB 83 (Linux)
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/dev/sda2 / 10GB 83 (Linux)
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/dev/sda3 swap 2GB 82 (Swap)
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/dev/sda4 LVM remainder 8e (LVM)
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/dev/sdb1 swap 2GB 82 (Swap)
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/dev/sdb2 LVM remainder 8e (LVM)</literal></screen>
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<para>First initialize the physical volumes:</para>
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<screen><userinput>pvcreate /dev/sda4 /dev/sdb2</userinput></screen>
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<para>Next create a volume group named lfs-lvm:</para>
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<screen><userinput>vgcreate lfs-lvm /dev/sda4 /dev/sdb2</userinput></screen>
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<para>The status of the volume group can be checked by running the command
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<command>vgscan</command>. Now create the logical volumes. Since there is
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about 3900 GB available, leave about 900 GB free for expansion. Note that the
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logical volume named <emphasis>mysql</emphasis> is larger than any physical
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disk. </para>
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<screen><userinput>lvcreate --name mysql --size 2500G lfs-lvm
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lvcreate --name home --size 500G lfs-lvm</userinput></screen>
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<para>Finally the logical volumes can be formatted and mounted. In this
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example, the jfs file system (<xref linkend='jfsutils'/>) is used for
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demonstration purposes.</para>
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<screen><userinput>mkfs -t ext4 /dev/lfs-lvm/home
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mkfs -t jfs /dev/lfs-lvm/mysql
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mount /dev/lfs-lvm/home /home
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mkdir -p /srv/mysql
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mount /dev/lfs-lvm/mysql /srv/mysql</userinput></screen>
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<para>The LFS boot scripts automatically make these file systems available
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to the system in the checkfs script. Edit the <filename>/etc/fstab</filename>
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file as required to automatically mount them.</para>
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<para>A LVM logical volume can host a root filesystem, but requires the use
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of an initramfs (initial RAM file system) and is not discussed here.</para>
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<para>For a more information about LVM, see the <ulink
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url="http://www.tldp.org/HOWTO/LVM-HOWTO/">LVM HOWTO</ulink> and
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the lvm man pages.</para>
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</sect1>
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