1 | <?xml version="1.0" encoding="ISO-8859-1"?>
|
---|
2 | <!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
|
---|
3 | "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
|
---|
4 | <!ENTITY % general-entities SYSTEM "../../general.ent">
|
---|
5 | %general-entities;
|
---|
6 | ]>
|
---|
7 |
|
---|
8 | <sect1 id="aboutlvm">
|
---|
9 | <?dbhtml filename="aboutlvm.html"?>
|
---|
10 |
|
---|
11 | <sect1info>
|
---|
12 | <othername>$LastChangedBy$</othername>
|
---|
13 | <date>$Date$</date>
|
---|
14 | </sect1info>
|
---|
15 |
|
---|
16 | <title>About Logical Volume Management (LVM)</title>
|
---|
17 |
|
---|
18 | <para>LVM manages disk drives. It allows multiple drives and partitions
|
---|
19 | to be combined into larger <emphasis>volume groups</emphasis>, assists in
|
---|
20 | making backups through a <emphasis>snapshot</emphasis>, and allows for
|
---|
21 | dynamic volume resizing. It can also provide mirroring similar to
|
---|
22 | a RAID 1 array.</para>
|
---|
23 |
|
---|
24 | <para>A complete discussion of LVM is beyond the scope of this introduction,
|
---|
25 | but basic concepts are presented below.</para>
|
---|
26 |
|
---|
27 | <para>To run any of the commands presented here, the <xref linkend='lvm2'/>
|
---|
28 | package must be installed. All commands must be run as the <systemitem
|
---|
29 | class="username">root</systemitem> user.</para>
|
---|
30 |
|
---|
31 | <para>Management of disks with lvm is accomplished using the following
|
---|
32 | concepts: </para>
|
---|
33 |
|
---|
34 | <variablelist>
|
---|
35 | <varlistentry>
|
---|
36 | <term>physical volumes</term>
|
---|
37 | <listitem><para>These are physical disks or partitions such as
|
---|
38 | /dev/sda3 or /dev/sdb.</para></listitem>
|
---|
39 | </varlistentry>
|
---|
40 |
|
---|
41 | <varlistentry>
|
---|
42 | <term>volume groups</term>
|
---|
43 | <listitem><para>These are named groups of physical volumes that
|
---|
44 | can be manipulated by the administrator. The number of physical
|
---|
45 | volumes that make up a volume group is arbitrary. Physical volumes
|
---|
46 | can be dynamically added or removed from a volume group.
|
---|
47 | </para></listitem>
|
---|
48 | </varlistentry>
|
---|
49 |
|
---|
50 | <varlistentry>
|
---|
51 | <term>logical volumes</term>
|
---|
52 | <listitem><para>Volume groups may be subdivided into logical volumes.
|
---|
53 | Each logical volume can then be individually formatted as if it were a
|
---|
54 | regular Linux partition. Logical volumes may be dynamically resized by
|
---|
55 | the administrator according to need.</para></listitem>
|
---|
56 |
|
---|
57 | </varlistentry>
|
---|
58 | </variablelist>
|
---|
59 |
|
---|
60 | <para>To give a concrete example, suppose that you have two 2 TB disks.
|
---|
61 | Also suppose a really large amount of space is required for a very large database,
|
---|
62 | mounted on <filename class='directory'>/srv/mysql</filename>. This is what
|
---|
63 | the initial set of partitions would look like:</para>
|
---|
64 |
|
---|
65 | <screen><literal>Partition Use Size Partition Type
|
---|
66 | /dev/sda1 /boot 100MB 83 (Linux)
|
---|
67 | /dev/sda2 / 10GB 83 (Linux)
|
---|
68 | /dev/sda3 swap 2GB 82 (Swap)
|
---|
69 | /dev/sda4 LVM remainder 8e (LVM)
|
---|
70 | /dev/sdb1 swap 2GB 82 (Swap)
|
---|
71 | /dev/sdb2 LVM remainder 8e (LVM)</literal></screen>
|
---|
72 |
|
---|
73 | <para>First initialize the physical volumes:</para>
|
---|
74 |
|
---|
75 | <screen><userinput>pvcreate /dev/sda4 /dev/sdb2</userinput></screen>
|
---|
76 |
|
---|
77 | <para>Next create a volume group named lfs-lvm:</para>
|
---|
78 |
|
---|
79 | <screen><userinput>vgcreate lfs-lvm /dev/sda4 /dev/sdb2</userinput></screen>
|
---|
80 |
|
---|
81 | <para>The status of the volume group can be checked by running the command
|
---|
82 | <command>vgscan</command>. Now create the logical volumes. Since there is
|
---|
83 | about 3900 GB available, leave about 900 GB free for expansion. Note that the
|
---|
84 | logical volume named <emphasis>mysql</emphasis> is larger than any physical
|
---|
85 | disk. </para>
|
---|
86 |
|
---|
87 | <screen><userinput>lvcreate --name mysql --size 2500G lfs-lvm
|
---|
88 | lvcreate --name home --size 500G lfs-lvm</userinput></screen>
|
---|
89 |
|
---|
90 | <para>Finally the logical volumes can be formatted and mounted. In this
|
---|
91 | example, the jfs file system (<xref linkend='jfsutils'/>) is used for
|
---|
92 | demonstration purposes.</para>
|
---|
93 |
|
---|
94 | <screen><userinput>mkfs -t ext4 /dev/lfs-lvm/home
|
---|
95 | mkfs -t jfs /dev/lfs-lvm/mysql
|
---|
96 | mount /dev/lfs-lvm/home /home
|
---|
97 | mkdir -p /srv/mysql
|
---|
98 | mount /dev/lfs-lvm/mysql /srv/mysql</userinput></screen>
|
---|
99 |
|
---|
100 | <para>The LFS boot scripts automatically make these file systems available
|
---|
101 | to the system in the checkfs script. Edit the <filename>/etc/fstab</filename>
|
---|
102 | file as required to automatically mount them.</para>
|
---|
103 |
|
---|
104 | <para>A LVM logical volume can host a root filesystem, but requires the use
|
---|
105 | of an initramfs (initial RAM file system) and is not discussed here.</para>
|
---|
106 |
|
---|
107 | <para>For a more information about LVM, see the <ulink
|
---|
108 | url="http://www.tldp.org/HOWTO/LVM-HOWTO/">LVM HOWTO</ulink> and
|
---|
109 | the lvm man pages.</para>
|
---|
110 |
|
---|
111 | </sect1>
|
---|