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Now that we have a section in the Handbook on how to add swap space,

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point the "add swap space" FAQ there.
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Michael Lucas 2002-01-22 18:58:20 +00:00
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@ -6365,91 +6365,12 @@ C:\="DOS"</programlisting>
</question>
<answer>
<para>The best way is to increase the size of your swap partition,
or take advantage of this convenient excuse to add another
disk. The general rule of thumb is to have around 2x the swap
space as you have main memory. However, if you have a very
small amount of main memory you may want to configure swap
beyond that. It is also a good idea to configure sufficient
swap relative to anticipated future memory upgrades so you do
not have to futz with your swap configuration later.</para>
<para>Adding swap onto a separate disk makes things faster than
simply adding swap onto the same disk. As an example, if you
are compiling source located on one disk, and the swap is on
another disk, this is much faster than both swap and compile on
the same disk. This is true for SCSI disks specifically.</para>
<para>When you have several disks, configuring a swap partition on
each one is usually beneficial, even if you wind up putting
swap on a work disk. Typically, each fast disk in your system
should have some swap configured. FreeBSD supports up to 4
interleaved swap devices by default. When configuring multiple
swap partitions you generally want to make them all about the
same size, but people sometimes make their primary swap
partition larger in order to accommodate a kernel core dump. Your
primary swap partition must be at least as large as main memory
in order to be able to accommodate a kernel core.</para>
<para>IDE drives are not able to allow access to both drives on
the same channel at the same time (FreeBSD does not support mode
4, so all IDE disk I/O is <quote>programmed</quote>).
It is still suggested that you put your swap partition on a
separate driver, however: the drives are so cheap, it is not
worth worrying about.</para>
<para>Swapping over NFS is only recommended if you do not have a
local disk to swap to. Swapping over NFS is slow and
inefficient in FreeBSD releases prior to 4.x, but reasonably
fast in releases greater or equal to 4.0. Even so, it will be
limited to the network bandwidth available and puts an
additional burden on the NFS server.</para>
<para>Here is an example for 64Mb vn-swap
(<filename>/usr/swap0</filename>, though of course you can use
any name that you want).</para>
<para>Make sure your kernel was built with the line</para>
<programlisting>pseudo-device vn 1 #Vnode driver (turns a file into a device)</programlisting>
<para>in your config-file. The GENERIC kernel already contains
this.</para>
<orderedlist>
<listitem>
<para>create a vn-device</para>
<screen>&prompt.root; <userinput>cd /dev</userinput>
&prompt.root; <userinput>sh MAKEDEV vn0</userinput></screen>
</listitem>
<listitem>
<para>create a swapfile (<filename>/usr/swap0</filename>)</para>
<screen>&prompt.root; <userinput>dd if=/dev/zero of=/usr/swap0 bs=1024k count=64</userinput></screen>
</listitem>
<listitem>
<para>set proper permissions on (<filename>/usr/swap0</filename>)</para>
<screen>&prompt.root; <userinput>chmod 0600 /usr/swap0</userinput></screen>
</listitem>
<listitem>
<para>enable the swap file in <filename>/etc/rc.conf</filename></para>
<programlisting>swapfile="/usr/swap0" # Set to name of swapfile if aux swapfile desired.</programlisting>
</listitem>
<listitem>
<para>reboot the machine</para>
</listitem>
</orderedlist>
<para>To enable the swap file immediately, type</para>
<screen>&prompt.root; <userinput>vnconfig -e /dev/vn0b /usr/swap0 swap</userinput></screen>
<para>In the <ulink
url="../handbook/config-tuning.html">Configuration and
Tuning</ulink> section of the Handbook, you will find a
<ulink
url="../handbook/adding-swap-space.html">section</ulink>
describing how to do this.</para>
</answer>
</qandaentry>
</qandaset>