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#pragma section-numbers off #format html <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >Benefits of Logical Volume Management on a Small System</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK REL="HOME" TITLE="LVM HOWTO" HREF="index.html"><LINK REL="UP" TITLE="What is Logical Volume Management?" HREF="c172.html"><LINK REL="PREVIOUS" TITLE="What is Logical Volume Management?" HREF="c172.html"><LINK REL="NEXT" TITLE="Benefits of Logical Volume Management on a Large System" HREF="x209.html"></HEAD ><BODY CLASS="sect1" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#840084" ALINK="#0000FF" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" >LVM HOWTO</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="c172.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" >Chapter 2. What is Logical Volume Management?</TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="x209.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="sect1" ><H1 CLASS="sect1" ><A NAME="benefitsoflvmsmall" >2.2. Benefits of Logical Volume Management on a Small System</A ></H1 ><P > One of the difficult decisions facing a new user installing Linux

for the first time is how to partition the disk drive. The need to estimate just how much space is likely to be needed for system files and user files makes the installation more complex than is necessary and some users simply opt to put all their data into one large partition in an attempt to avoid the issue.

><P > Once the user has guessed how much space is needed for /home /usr /

(or has let the installation program do it) then is quite common for one of these partitions to fill up even if there is plenty of disk space in one of the other partitions.

><P > With logical volume management, the whole disk would be allocated

to a single volume group and logical volumes created to hold the / /usr and /home file systems. If, for example the /home logical volume later filled up but there was still space available on /usr then it would be possible to shrink /usr by a few megabytes and reallocate that space to /home.

><P > Another alternative would be to allocate minimal amounts of space

for each logical volume and leave some of the disk unallocated. Then, when the partitions start to fill up, they can be expanded as necessary.

><P > As an example:

Joe buys a PC with an 8.4 Gigabyte disk on it and installs Linux using the following partitioning system:
<PRE

CLASS="screen" > /boot /dev/hda1 10 Megabytes swap /dev/hda2 256 Megabytes / /dev/hda3 2 Gigabytes /home /dev/hda4 6 Gigabytes

</PRE

This, he thinks, will maximize the amount of space available for all his MP3 files.

><P > Sometime later Joe decides that he want to install the latest

office suite and desktop UI available but realizes that the root partition isn't large enough. But, having archived all his MP3s onto a new writable DVD drive there is plenty of space on /home.

><P > His options are not good:

><P ></P ><OL TYPE="1" ><LI ><P > Reformat the disk, change the partitioning scheme and

reinstall.

></LI ><LI ><P > Buy a new disk and figure out some new partitioning scheme

that will require the minimum of data movement.

></LI ><LI ><P > Set up a symlink farm on / pointing to /home and install the new

software on /home

></LI ></OL ><P > With LVM this becomes much easier:

><P > Jane buys a similar PC but uses LVM to divide up the disk in a similar

manner:

><PRE CLASS="screen" > /boot /dev/hda1 10 Megabytes swap /dev/vg00/swap 256 Megabytes / /dev/vg00/root 2 Gigabytes /home /dev/vg00/home 6 Gigabytes

</PRE

><DIV CLASS="note" ><P ></P ><TABLE CLASS="note" WIDTH="100%" BORDER="0" ><TR ><TD WIDTH="25" ALIGN="CENTER" VALIGN="TOP" ><IMG SRC="../images/note.gif" HSPACE="5" ALT="Note"></TD ><TD ALIGN="LEFT" VALIGN="TOP" ><P > boot is not included on the LV because bootloaders don't

understand LVM volumes yet. It's possible boot on LVM will work, but you run the risk of having an unbootable system.

></TD ></TR ></TABLE ></DIV ><DIV CLASS="warning" ><P ></P ><TABLE CLASS="warning" WIDTH="100%" BORDER="0" ><TR ><TD WIDTH="25" ALIGN="CENTER" VALIGN="TOP" ><IMG SRC="../images/warning.gif" HSPACE="5" ALT="Warning"></TD ><TH ALIGN="LEFT" VALIGN="MIDDLE" ><B >root on LV should be used by advanced users only</B ></TH ></TR ><TR ><TD > </TD ><TD ALIGN="LEFT" VALIGN="TOP" ><P > root on LVM requires an initrd image that activates the root

LV. If a kernel is upgraded without building the necessary initrd image, that kernel will be unbootable. Newer distributions support lvm in their mkinitrd scripts as well as their packaged initrd images, so this becomes less of an issue over time.

></TD ></TR ></TABLE ></DIV ><P > When she hits a similar problem she can reduce the size of /home by

a gigabyte and add that space to the root partition.

><P > Suppose that Joe and Jane then manage to fill up the /home

partition as well and decide to add a new 20 Gigabyte disk to their systems.

><P > Joe formats the whole disk as one partition (/dev/hdb1) and moves

his existing /home data onto it and uses the new disk as /home. But he has 6 gigabytes unused or has to use symlinks to make that disk appear as an extension of /home, say /home/joe/old-mp3s.

><P > Jane simply adds the new disk to her existing volume group and

extends her /home logical volume to include the new disk. Or, in fact, she could move the data from /home on the old disk to the new disk and then extend the existing root volume to cover all of the old disk.

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