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<sect3 id="lvmcfg">
<title>Configuring Logical Volume Manager (LVM)</title>
<para>
If you are working with computers at the level of system administrator
or <quote>advanced</quote> user, you have surely seen the situation
where some disk partition (usually the most important one) was short on
space, while some other partition was grossly underused and you had to
manage this situation with moving stuff around, symlinking, etc.
</para><para>
To avoid the described situation you can use Logical Volume Manager
(LVM). Simply said, with LVM you can combine your partitions
(<firstterm>physical volumes</firstterm> in LVM lingo) to form
a virtual disc (so called <firstterm>volume group</firstterm>), which
can then be divided into virtual partitions (<firstterm>logical
volumes</firstterm>). The point is that logical volumes (and of course
underlying volume groups) can span across several physical discs.
</para><para>
Now when you realize you need more space for your old 160GB
<filename>/home</filename> partition, you can simply add a new 300GB
disc to the computer, join it with your existing volume group and then
resize the logical volume which holds your <filename>/home</filename>
filesystem and voila — your users have some room again on their
renewed 460GB partition. This example is of course a bit
oversimplified. If you haven't read it yet, you should consult the
<ulink url="&url-lvm-howto;">LVM HOWTO</ulink>.
</para><para>
LVM setup in &d-i; is quite simple. At first, you have to mark your
partitions to be used as physical volumes for LVM. (This is done in
<command>partman</command> in the <guimenu>Partition
settings</guimenu> menu where you should select <menuchoice>
<guimenu>Use as:</guimenu> <guimenuitem>physical volume for
LVM</guimenuitem> </menuchoice>.) Then start the
<command>lvmcfg</command> module (either directly from
<command>partman</command> or from the &d-i;'s main menu) and combine
physical volumes to volume group(s) under the <guimenuitem>Modify
volume groups (VG)</guimenuitem> menu. After that, you should create
logical volumes on the top of volume groups from the menu
<guimenuitem>Modify logical volumes (LV)</guimenuitem>.
<note arch="powerpc" condition="sarge"><para>
There is no widely accepted standard to identify partitions containing
LVM data on Apple Power Macintosh hardware. On this particular
hardware, the above procedure for creating physical volumes and volume
groups will not work. There is a good workaround for this limitation,
provided you are familiar with the underlying LVM tools.
</para><para>
To install using logical volumes on Power Macintosh hardware you
should create all the disk partitions for your logical volumes as
usual. In the <guimenu>Partition settings</guimenu> menu you should
choose <menuchoice><guimenu>Use as:</guimenu> <guimenuitem>Do Not
Use</guimenuitem></menuchoice> for these partitions (you will not be
offered the option to use the partition as a physical volume). When
you are done with creating all your partitions, you should start the
logical volume manager as usual. However, since no physical volumes
have been created you must now access the command shell available on
the second virtual terminal (see <xref linkend="shell"/>) and create
them manually.
</para><para>
Use the <command>pvcreate</command> command at the shell command prompt
to create a physical volume on each of your chosen partitions. Then use
the <command>vgcreate</command> command to create each volume group
you want. You can safely ignore any errors about incorrect metadata
area header checksums and fsync failures while doing this. When you
have finished creating all your volume groups, you should go back to
the first virtual terminal and skip directly to the
<command>lvmcfg</command> menu items for logical volume
management. You will see your volume groups and you can create the
logical volumes you need as usual.
</para></note>
</para><para>
After returning from <command>lvmcfg</command> back to
<command>partman</command>, you will see any created logical volumes
in the same way as ordinary partitions (and you should treat them like
that).
</para>
</sect3>
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