Sharpe, Sam J wrote:
2009/8/20 Pasi Kärkkäinen <pasik@xxxxxx>:
On Thu, Aug 20, 2009 at 01:43:27PM -0700, Phill wrote:
I'm rebuilding a RHEL 5 server used primarily for building code.
It has perc 6i controller and I'm installing 6 15K sas drives.
The plan is to setup a raid 10 configuration for improved performance.
Does anyone know if I can significantly increase or degrade my performance
by selecting a larger stripe size? The default is 64k and I have read in a
performance report that a 512k size may be more desirable for Linux systems.
Thanks for any replies.
Well.. if you do large sequential reads/writes then big stripe size will
help, but if you do small random-io then large stripe size like that will be
really bad.
It really depends on your workload.
I was about to say much the same thing in closing, but actually was
going to point you to this article which has different advice to
Pasi's (and different to how I would expect).
http://www.pcguide.com/ref/hdd/perf/raid/concepts/perfStripe-c.html
It actually says that a large stripe size might be better for random
transactions on lots of small files (as I would expect from compiling
code), because it means you can read a whole small file from each disk
in the array - so in your case you'd be able to read 6 files at once
(1 from each stripe (3) multiplied by 2 (for the mirrored copies)). If
you had a small stripe size, you'd increase the chance that your small
file would be split across multiple disks - so you might require more
than one disk per file and you wouldn't get 6 concurrent accesses - in
your case it might involve up to three drives.
A small number of requests for large files might benefit from small
stripe sizes, because it would increase the chance that reading your
large file involved reads from multiple disks - so you'd get higher
throughput.
Which is fine for read-only use, while it may hurt your write. Also note that
many controllers use the term "raid-10" when they really mean "raid 1+0" which
isn't the same at all as Linux software raid-10.
As always, "large" and "small" file sizes are subjective terms and
there is no substitute for benchmarking your own particular case - and
this is a hotly contested subject among Storage gurus!
Hell, people can't even agree on what the terms mean, in some cases.
--
Bill Davidsen <davidsen@xxxxxxx>
"We have more to fear from the bungling of the incompetent than from
the machinations of the wicked." - from Slashdot
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