106 lines
4.1 KiB
HTML
106 lines
4.1 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
|
|
<HTML>
|
|
<HEAD>
|
|
<META NAME="GENERATOR" CONTENT="SGML-Tools 1.0.9">
|
|
<TITLE>HOWTO: Multi Disk System Tuning: Advanced Issues</TITLE>
|
|
<LINK HREF="Multi-Disk-HOWTO-15.html" REL=next>
|
|
<LINK HREF="Multi-Disk-HOWTO-13.html" REL=previous>
|
|
<LINK HREF="Multi-Disk-HOWTO.html#toc14" REL=contents>
|
|
</HEAD>
|
|
<BODY>
|
|
<A HREF="Multi-Disk-HOWTO-15.html">Next</A>
|
|
<A HREF="Multi-Disk-HOWTO-13.html">Previous</A>
|
|
<A HREF="Multi-Disk-HOWTO.html#toc14">Contents</A>
|
|
<HR>
|
|
<H2><A NAME="s14">14. Advanced Issues</A></H2>
|
|
|
|
<P>
|
|
<!--
|
|
disk!advanced topics
|
|
-->
|
|
|
|
Linux and related systems offer plenty of possibilities for fast, efficient
|
|
and devastating destruction. This document is no exception. With power comes
|
|
dangers and the following sections describe a few more esoteric issues that
|
|
should not be attempted before reading and understanding the documentation,
|
|
the issues and the dangers. You should also make a backup. Also remember
|
|
to try to restore the system from scratch from your backup at least once.
|
|
Otherwise you might not be the first to be found with a perfect backup of
|
|
your system and no tools available to reinstall it (or, even more
|
|
embarrassing, some critical files missing on tape).
|
|
<P>The techniques described here are rarely necessary but can be used for very
|
|
specific setups. Think very clearly through what you wish to accomplish
|
|
before playing around with this.
|
|
<P>
|
|
<H2><A NAME="ss14.1">14.1 Hard Disk Tuning</A>
|
|
</H2>
|
|
|
|
<P>
|
|
<!--
|
|
disk!advanced topics!tuning, hard disk
|
|
-->
|
|
|
|
The hard drive parameters can be tuned using the <CODE>hdparms</CODE> utility. Here
|
|
the most interesting parameter is probably the read-ahead parameter which
|
|
determines how much prefetch should be done in sequential reading.
|
|
<P>If you want to try this out it makes most sense to tune for the
|
|
characteristic file size on your drive but remember that this tuning is for
|
|
the <EM>entire</EM> drive which makes it a bit more difficult. Probably this is
|
|
only of use on large servers using dedicated news drives etc.
|
|
<P>For safety the default hdparm settings are rather conservative. The
|
|
disadvantage is that this mean you can get lost interrupts if you have
|
|
a high frequency of IRQs as you would when using the serial port and
|
|
an IDE disk as IRQs from the latter would mask other IRQs. This would
|
|
be noticeable as less then ideal performance when downloading data from
|
|
the net to disk. Setting <CODE>hdparm -u1 device</CODE> would prevent this
|
|
masking and either improve your performance or, depending on hardware,
|
|
corrupt the data on your disk. Experiment with caution and fresh
|
|
backups.
|
|
<P>For more information read the article
|
|
<A HREF="http://www.linuxforum.com/plug/articles/needforspeed.html">The Need For Speed</A>
|
|
on tuning with <CODE>hdparm</CODE>.
|
|
<P>
|
|
<P>
|
|
<H2><A NAME="ss14.2">14.2 File System Tuning</A>
|
|
</H2>
|
|
|
|
<P>
|
|
<!--
|
|
disk!advanced topics!tuning, filesystem
|
|
-->
|
|
|
|
Most file systems come with a tuning utility and for <CODE>ext2fs</CODE> there is
|
|
the <CODE>tune2fs</CODE> utility. Several parameters can be modified but perhaps
|
|
the most useful parameter here is what size should be reserved and who should
|
|
be able to take advantage of this which could help you getting more useful
|
|
space out of your drives, possibly at the cost of less room for repairing
|
|
a system should it crash.
|
|
<P>
|
|
<P>
|
|
<H2><A NAME="ss14.3">14.3 Spindle Synchronizing</A>
|
|
</H2>
|
|
|
|
<P>
|
|
<!--
|
|
disk!advanced topics!spindle synchronization
|
|
-->
|
|
|
|
This should not in itself be dangerous, other than the peculiar fact that
|
|
the exact details of the connections remain unclear for many drives. The
|
|
theory is simple: keeping a fixed phase difference between the different
|
|
drives in a RAID setup makes for less waiting for the right track to come
|
|
into position for the read/write head. In practice it now seems that with
|
|
large read-ahead buffers in the drives the effect is negligible.
|
|
<P>Spindle synchronisation should not be used on RAID0 or RAID 0/1 as you
|
|
would then lose the benefit of having the read heads over different
|
|
areas of the mirrored sectors.
|
|
<P>
|
|
<P>
|
|
<P>
|
|
<HR>
|
|
<A HREF="Multi-Disk-HOWTO-15.html">Next</A>
|
|
<A HREF="Multi-Disk-HOWTO-13.html">Previous</A>
|
|
<A HREF="Multi-Disk-HOWTO.html#toc14">Contents</A>
|
|
</BODY>
|
|
</HTML>
|