/usr/share/doc/sysadmin-guide/html/alloc-disk.html

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><A
NAME="ALLOC-DISK"
></A
>5.12. Allocating disk space</H1
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="PART-SCHEMES"
></A
>5.12.1. Partitioning schemes</H2
><P
>When it comes to partitioning your machine, 
	there is no universally correct way to do it. There are
	many factors that must be taken into account depending on 
	the purpose of the machine.</P
><P
>For a simple workstation with limited disk space, such 
	as a laptop, you may have as few a 3 partitions.  A partition for
	<TT
CLASS="FILENAME"
>/</TT
>, <TT
CLASS="FILENAME"
>/boot</TT
>, and swap.
	However, for most users this is not a recommended solution.</P
><P
>&#13;	</P
><P
>The traditional way is to have a (relatively) small
	root filesystem, and separate partitions for filesystems such as 
	<TT
CLASS="FILENAME"
>/usr</TT
> and <TT
CLASS="FILENAME"
>/home&#62;</TT
>.
	Creating a separate root filesystem if the root filesystem is small and 
	not heavily used, it is less likely to become corrupt when the system
	crashes, and therefore make it easier to recover a crashed system.  The
	reason is to prevent having the root filesystem get filled and cause a 
	system crash.</P
><P
>When creating your partitioning scheme, there are some things you 
	need to remember.  You cannot create separate partitions for the following 
	directories: <TT
CLASS="FILENAME"
>/bin</TT
>, <TT
CLASS="FILENAME"
>/etc</TT
>, 
	<TT
CLASS="FILENAME"
>/dev</TT
>, <TT
CLASS="FILENAME"
>/initrd</TT
>, 
	<TT
CLASS="FILENAME"
>/lib</TT
>, and <TT
CLASS="FILENAME"
>/sbin</TT
>.  The
	contents of these directories are required at bootup and must
	always be part of the <TT
CLASS="FILENAME"
>/</TT
> partition.</P
><P
>It is also recommended that you create separate partitions for 
	<TT
CLASS="FILENAME"
>/var</TT
> and <TT
CLASS="FILENAME"
>/tmp</TT
>.  This is
	because both directories typically have data that is constantly 
	changing.  Not creating separate partitions for these filesystems
	puts you at risk of having log file fill up our <TT
CLASS="FILENAME"
>/</TT
>
	partition.</P
><P
>An example of a server partition is:
	<TABLE
BORDER="1"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="SCREEN"
><TT
CLASS="COMPUTEROUTPUT"
>Filesystem            Size  Used Avail Use% Mounted on
/dev/hda2             9.7G  1.3G  8.0G  14% /
/dev/hda1             128M   44M   82M  34% /boot
/dev/hda3             4.9G  4.0G  670M  86% /usr
/dev/hda5             4.9G  2.1G  2.5G  46% /var
/dev/hda7              31G   24G  5.6G  81% /home
/dev/hda8             4.9G  2.0G  670M  43% /opt
	</TT
></PRE
></FONT
></TD
></TR
></TABLE
></P
><P
>The problem with having many partitions is that it splits
	the total amount of free disk space into many small pieces.  One way
	to avoid this problem is to use to create Logical Volumes.</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="LVM"
></A
>5.12.2. Logical Volume Manager (LVM)</H2
><P
>Using LVM allows administrators the flexibility to create 
	logical disks that can be expanded dynamically as more disk space 
	is required.</P
><P
>This is done first by creating partitions with as an 
	0x8e Linux LVM partition type.  Then the <I
CLASS="GLOSSTERM"
>Physical Partitions
	</I
> are added to a <I
CLASS="GLOSSTERM"
>Volume Group</I
> and 
	broken up into chunks, or <I
CLASS="GLOSSTERM"
>Physical Extents</I
>
	<I
CLASS="GLOSSTERM"
>Volume Group</I
>. These extends can then be grouped
	into <I
CLASS="GLOSSTERM"
>Logical Volumes</I
>.  These Logical Volumes 
	then can be formatted just like a physical partition.  The big 
	difference is that they can be expanded by adding more extents to 
	them.</P
><P
>Right now, a full discussion of LVM is beyond the scope of this 
	guide.  However, and excellent resource for learning more about LVM
	can be found at <A
HREF="http://www.tldp.org/HOWTO/LVM-HOWTO.html"
TARGET="_top"
>	http://www.tldp.org/HOWTO/LVM-HOWTO.html</A
>.</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="SPACE-REQ"
></A
>5.12.3. Space requirements</H2
><P
>The Linux distribution you install will give some indication
	of how much disk space you need for various configurations. Programs
	installed separately may also do the same.  This will help you plan
	your disk space usage, but you should prepare for the future and
	reserve some extra space for things you will
	notice later that you need.</P
><P
>The amount you need for user files depends on what your
	users wish to do.  Most people seem to need as much space for their
	files as possible, but the amount they will live happily with varies
	a lot.  Some people do only light text processing and will survive
	nicely with a few megabytes, others do heavy
	image processing and will need gigabytes.</P
><P
>By the way, when comparing file sizes given in
	kilobytes or megabytes and disk space given in megabytes, it can be
	important to know that the two units can be different. Some disk
	manufacturers like to pretend that a kilobyte is 1000 bytes and a
	megabyte is 1000 kilobytes, while all the rest of the computing
	world uses 1024 for both factors.  Therefore, a 345 MB hard disk
	is really a 330 MB hard disk.</P
><P
>Swap space allocation is discussed in <A
HREF="swap-allocation.html"
>Section 6.5</A
>.</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="ALLOC-SPACE-EX"
></A
>5.12.4. Examples of hard disk allocation</H2
><P
>I used to have a 10 GB hard disk.  Now I am using a 30 GB
	hard disk.  I'll explain how and why I partitioned those
	disks.</P
><P
>First, I created a <TT
CLASS="FILENAME"
>/boot</TT
> partition 
	at 128 MG.  This is larger than I will need, and big enough to
	give me space if I need it.  I created a separate 
	<TT
CLASS="FILENAME"
>/boot</TT
> partition to ensure that this 
	filesystem will never get filled up, and therefore will be 
	bootable.  Then I created a 5 GB <TT
CLASS="FILENAME"
>/var</TT
> 
	partition.  Since the <TT
CLASS="FILENAME"
>/var</TT
> filesystem is 
	where log files and email is stored I wanted to isolate it
	from my root partition.  (I have had log files grow overnight 
	and fill my root filesystem in the past.) Next, I created a 15 GB 
	<TT
CLASS="FILENAME"
>/home</TT
> partition.  This is handy in the event 
	of a system crash.  If I ever have to re-install Linux from scratch, 
	I can tell the installation program to not format this partition, and
	instead remount it without the data being lost. Finally 
	since I had 512 MG of RAM I created a 1024 MG (or 1 GB) swap 
	partition.  This left me with roughly a 9 GB root filesystem.  I using 
	my old 10 GB hard drive, I created an 8 GB <TT
CLASS="FILENAME"
>/usr</TT
> 
	partition and left 2 GB unused.  This is incase I need more space  
	in the future.</P
><P
>In the end, my partition tables looked like this:

		<DIV
CLASS="TABLE"
><A
NAME="AEN3270"
></A
><P
><B
>Table 5-3. My Partitions</B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><TBODY
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>9 GB</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>root filesystem</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>1 GB</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>swap partition</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>5 GB</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="FILENAME"
>/var</TT
> 
		filesystem</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>15 GB</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="FILENAME"
>/home</TT
> 
		filesystem</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
> 8 GB</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="FILENAME"
>/usr</TT
>
		filesystem</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
> 2 GB</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>scratch partition</TD
></TR
></TBODY
></TABLE
></DIV
>
	</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="ADDING-DISK"
></A
>5.12.5. Adding more disk space for Linux</H2
><P
>Adding more disk space for Linux is easy, at least after the
	hardware has been properly installed  (the hardware installation
	is outside the scope of this book).  You format it if necessary,
	then create the partitions and filesystem as described above,
	and add the proper lines to <TT
CLASS="FILENAME"
>/etc/fstab</TT
>
	
	so that it is mounted automatically.</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="SPACE-SAVING-TIPS"
></A
>5.12.6. Tips for saving disk space</H2
><P
>The best tip for saving disk space is to avoid installing
	unnecessary programs.  Most Linux distributions have an
	option to install only part of the packages they contain,
	and by analyzing your needs you might notice that you don't
	need most of them.  This will help save a lot of disk space,
	since many programs are quite large.  Even if you do need a
	particular package or program, you might not need all of it.
	For example, some on-line documentation might be unnecessary,
	as might some of the Elisp files for GNU Emacs, some of the
	fonts for X11, or some of the libraries for programming.</P
><P
>If you cannot uninstall packages, you might look into
	compression.  Compression programs such as <B
CLASS="COMMAND"
>gzip</B
>
	
	or <B
CLASS="COMMAND"
>zip</B
>
	 will compress (and uncompress)
	individual files or groups of files.  The <B
CLASS="COMMAND"
>gzexe</B
>
	
	system will compress and uncompress programs invisibly to the
	user (unused programs are compressed, then uncompressed as they
	are used).  The experimental DouBle system will compress all
	files in a filesystem, invisibly to the programs that use them.
	(If you are familiar with products such as Stacker for MS-DOS 
	or DriveSpace for Windows, the principle is the same.)</P
><P
>Another way to save space is to take special care when 
	formatting you partitions.  Most modern filesystems will allow
	you to specify the block size.  The block size is chunk size that 
	the filesystem will use to read and write data.  Larger block sizes
	will help disk I/O performance when using large files, such as databases.
	This happens because the disk can read or write data for a longer 
	period of time before having to search for the next block.  The  
		&#13;</P
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