MD1000-PERC5/E Performance issues

[Mike McGrath]

On Sun, 28 Dec 2008, Mike McGrath wrote:

> I've read up on:
> http://thias.marmotte.net/archives/2008/01/05/Dell-PERC5E-and-MD1000-performance-tweaks.html
>
> Which seems to have helped but I really don't think I'm seeing the
> performance data I should be.  Take the attached sar data.  I started by
> doing a recursive cp of some files from the filesystem to some other
> drives, then started the sar dump.
>
> At marker 12:12:55, I started to do a cat /dev/sde > /dev/null.  (/dev/sde
> is the array).
>
> Why was there such a significant jump there?  Also, why does sar think the
> array was 100% utilized basically the whole time even though there's such
> a difference in sec reads/s?
>
> Other issues.  /dev/sde is the underlying physical device (raid5).
> However, it is divided up using lvm.  The copy mentioned above was from
> a logical volume.  While I expected some overhead and performance hit, I
> didn't expect it to be so huge and sporadic.  I've seen reads as low as
> 3MB/s during a copy.
>
> Thoughts?
>

Ok, upon further testing I don't think the majority of my issue is related
to the MD1000 or the raid controller.  I'm seeing decent read speeds from
large files.  So I'll get back to debugging unless someone has a tip.  I
suspect another list would be better.

	-Mike