RE: [squid-users] RE: Disk Configuration

Every time something is written to disk, parity information must be updated.
Using iostat will show just how often writes occur. The same general
problem holds true for a mirrored (RAID 1) setup.

Striping (RAID 0) will not likely harm Squid's performance, unless one of
the drives dies (trashing the whole cache), but it won't likely help much
more than spreading your cache dirs across multiple disks and letting Squid
worry about the details.

Here is a study (from 1996) on whether RAID is worthwhile:

http://www.google.com/search?q=cache:f-rlyGxkQxkJ:archive.nlm.nih.gov/pubs/b
angbuck/bangbuck.php&hl=en&lr=&strip=1

Obviously prices have dropped, so cost doesn't factor as much, but the
timeless bits are:

"For applications where fault tolerance is required, and retrieval speeds
can be slower than those available from hardware alone, RAID 5 is the best
choice. For RAID 5, wider stripes appear to improve both sequential access
speed and concurrent access speed for files in this range."

and

"For applications where fault tolerance is not important and funds are
limited, balancing the load across several volumes without the benefit of
RAID management can yield fast retrieval speeds at significant cost savings.

We find no reasons for choosing RAID 0 for applications involving small
files. The slight performance advantage for sequential file retrieval is
offset by the cost of the RAID management capabilities and the reliability
risk incurred by distributing each file across several disks."

If you have the time and the resources, I'd love to see a study where
Squid's cache dir is placed on various RAID arrays (both hardware and
software) and performance measured.

Chris

-----Original Message-----
From: William Stucke [mailto:William@zanet.co.za]
Sent: Monday, November 29, 2004 1:23 PM
To: squid-users@squid-cache.org
Subject: RE: [squid-users] RE: Disk Configuration

Adam Aube said: -

> The only caution about RAID I have seen is that RAID-5 will kill disk
performance with Squid (due to its usage profile)

How? Why? Please explain. Just because the FAQ says so doesn't make it true,
or explain why.

Kind regards,

William Stucke
ZAnet Internet Services (Pty) Ltd
+27 11 465 0700
William@zanet.co.za

-----Original Message-----
From: news [mailto:news@sea.gmane.org]On Behalf Of Adam Aube
Sent: 29 November 2004 23:28
To: squid-users@squid-cache.org
Subject: [squid-users] RE: Disk Configuration

Chris Robertson wrote:

> Everything I've read says that you should not use any RAID for your cache
> directories. Make a bunch of cache dirs (each on its own disk), and let
> Squid sort it out.

The only caution about RAID I have seen is that RAID-5 will kill disk
performance with Squid (due to its usage profile). I don't know if RAID-1
and RAID-10 are similarly affected.

For best disk performance you should use several smaller disks and have
Squid setup a cache dir on each one (no RAID).

Adam
Received on Mon Nov 29 2004 - 16:05:24 MST