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<sect2 id="lvm" status="review">
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<title>Logical Volume Manager (LVM)</title>
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Logical Volume Manger, or <emphasis>LVM</emphasis>, allows administrators to create <emphasis>logical</emphasis> volumes out of
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one or multiple physical hard disks. LVM volumes can be created on both software RAID partitions and standard partitions
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residing on a single disk. Volumes can also be extended, giving greater flexibility to systems as requirements change.
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<sect3 id="lvm-overview" status="review">
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<title>Overview</title>
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A side effect of LVM's power and flexibility is a greater degree of complication. Before diving into the LVM installation process,
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it is best to get familiar with some terms.
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<emphasis>Volume Group (VG):</emphasis> contains one or several Logical Volumes (LV).
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<emphasis>Logical Volume (LV):</emphasis> is similar to a partition in a non-LVM system. Multiple Physical Volumes (PV)
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can make up one LV, on top of which resides the actual EXT3, XFS, JFS, etc filesystem.
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<emphasis>Physical Volume (PV):</emphasis> physical hard disk or software RAID partition. The Volume Group can be extended
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<sect3 id="lvm-installation" status="review">
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<title>Installation</title>
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As an example this section covers installing Ubuntu Server Edition with <filename role="directory">/srv</filename> mounted
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on a LVM volume. During the initial install only one Physical Volume (PV) will be part of the Volume Group (VG). Another
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PV will be added after install to demonstrate how a VG can be extended.
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There are several installation options for LVM, <emphasis>"Guided - use the entire disk and setup LVM"</emphasis>,
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<emphasis>"Guided - use entire and setup encrypted LVM"</emphasis>, or <emphasis>Manually</emphasis> setup the partitions
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and configure LVM. At this time the only way to configure a system with both LVM and standard partitions, during installation,
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is to use the Manual approach.
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Follow the installation steps until you get to the <emphasis>Partition disks</emphasis> step, then:
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At the <emphasis>"Partition Disks</emphasis> screen choose <emphasis>"Manual"</emphasis>.
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Select the hard disk and on the next screen choose "yes" to <emphasis>"Create a new empty partition table on this device"</emphasis>.
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Next, create standard <emphasis>/boot</emphasis>, <emphasis>swap</emphasis>, and <emphasis>/</emphasis> partitions with whichever
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filesystem you prefer.
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For the LVM <emphasis>/srv</emphasis>, create a new <emphasis>Logical</emphasis> partition. Then change <emphasis>"Use as"</emphasis>
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to <emphasis>"physical volume for LVM"</emphasis> then <emphasis>"Done setting up the partition"</emphasis>.
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Now select <emphasis>"Configure the Logical Volume Manager"</emphasis> at the top, and choose <emphasis>"Yes"</emphasis> to write
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For the <emphasis>"LVM configuration action"</emphasis> on the next screen, choose <emphasis>"Create volume group"</emphasis>. Enter
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a name for the VG such as <emphasis>vg01</emphasis>, or something more descriptive. After entering a name, select the partition
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configured for LVM, and choose <emphasis>"Continue"</emphasis>.
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Back at the <emphasis>"LVM configuration action"</emphasis> screen, select <emphasis>"Create logical volume"</emphasis>. Select
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the newly created Logical Volume, and enter a name for the new LV, for example <emphasis>srv</emphasis> since that is the intended
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mount point. Then choose a size, which may be the full partition because it can always be extended later. Choose
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<emphasis>"Finish"</emphasis> and you should be back at the main <emphasis>"Partition Disks"</emphasis> screen.
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Now add a filesystem to the new LVM. Select the partition under <emphasis>"LVM VG vg01, LV srv"</emphasis>, or whatever name
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you have chosen, the choose <emphasis>Use as</emphasis>. Setup a file system as normal selecting <emphasis>/srv</emphasis> as
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the mount point. Once done, select <emphasis>"Done setting up the partition"</emphasis>.
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Finally, select <emphasis>"Finish partitioning and write changes to disk"</emphasis>. Then confirm the changes and continue
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with the rest of the installation.
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There are some useful utilities to view information about LVM:
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<listitem><para><emphasis>vgdisplay:</emphasis> shows information about Volume Groups.</para></listitem>
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<listitem><para><emphasis>lvdisplay:</emphasis> has information about Logical Volumes.</para></listitem>
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<listitem><para><emphasis>pvdisplay:</emphasis> similarly displays information about Physical Volumes.</para></listitem>
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<sect3 id="lvm-extending" status="review">
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<title>Extending Volume Groups</title>
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Continuing the <emphasis>/srv</emphasis> as an LVM volume example, this section covers adding a second Physical Volume (PV) to
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<filename role="directory">/srv</filename> and expanding the filesystem. This example assumes a second hard disk has been added
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to the system and will be added to the <emphasis>vg01</emphasis> volume group.
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First, create a partition on the new disk using the <application>fdisk</application> utility. For example,
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from a terminal enter:
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<command>sudo fdisk /dev/sdb</command>
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<computeroutput>Device contains neither a valid DOS partition table, nor Sun, SGI or OSF disklabel
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Building a new DOS disklabel with disk identifier 0x7b741e03.
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Changes will remain in memory only, until you decide to write them.
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After that, of course, the previous content won't be recoverable.
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Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)
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Command (m for help): <userinput>n</userinput>
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p primary partition (1-4)
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<userinput>p</userinput>
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Partition number (1-4): <userinput>1</userinput>
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First cylinder (1-391, default 1):
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Using default value 1
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Last cylinder, +cylinders or +size{K,M,G} (1-391, default 391):
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Using default value 391
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Command (m for help): <userinput>w</userinput>
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The partition table has been altered!
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Calling ioctl() to re-read partition table.
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Syncing disks.</computeroutput>
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The above output creates a single partition covering the entire disk. Your output will vary depending on your hard disk.
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A quick <application>fdisk</application> reference:
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<listitem><para><emphasis>n:</emphasis> creates a new partition.</para></listitem>
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<listitem><para><emphasis>p:</emphasis> prints the partition table.</para></listitem>
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<listitem><para><emphasis>w:</emphasis> writes the changes to disk, and exits fdisk.</para></listitem>
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<listitem><para><emphasis>q:</emphasis> quits fdisk without writing the changes to disk.</para></listitem>
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Adjust <filename>/dev/sdb</filename> according to your system. Also, the <application>cfdisk</application>,
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menu driven, partition utility can be used instead of <application>fdisk</application>.
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Next, create a Physical Volume (PV) on the new partition:
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<command>sudo pvcreate /dev/sdb1</command>
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Now extend the Volume Group (VG):
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<command>sudo vgextend vg01 /dev/sdb1</command>
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The Logical Volume (LV) can now be extended:
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<command>sudo lvextend /dev/vg01/srv -L3221M</command>
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The <emphasis>-L</emphasis> option allows the LV to be extended using Meg, Gig, Tera, etc bytes. Just be sure the
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hard disk has enough space for the value you choose. The <application>fdisk</application> <emphasis>q</emphasis>
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option will display the exact size of a drive.
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Finally, resize the filesystem:
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<command>sudo resize2fs /dev/vg01/srv</command>
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The above command is for an <application>EXT3</application> or <application>EXT4</application> filesystem. If you are
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using another filesystem there may be other resize utilities available.
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You should now see the expanded space in <filename>/srv</filename>: <command>df -h</command>.
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<sect3 id="lvm-resources" status="review">
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<title>Resources</title>
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See the <ulink url="http://tldp.org/HOWTO/LVM-HOWTO/index.html">LVM HOWTO</ulink> for more information.
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Another good article is
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<ulink url="http://www.linuxdevcenter.com/pub/a/linux/2006/04/27/managing-disk-space-with-lvm.html">Managing Disk Space with LVM</ulink>
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on O'Reilly's linuxdevcenter.com site.
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For more information on <application>fdisk</application> see the
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<ulink url="http://manpages.ubuntu.com/manpages/jaunty/en/man8/fdisk.8.html">fdisk man page</ulink>.
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serverguide/C/installation.xml
