Disk performance drop in new RHEL 5 kernel?

Peter Kjellstrom cap at nsc.liu.se
Fri Aug 27 04:55:00 CDT 2010

On Thursday 26 August 2010, Drew Weaver wrote:
> Hi there, I am testing some R510s /w PERC H700 that I am going to be using
> for storage systems.
> I am using a very basic benchmark (hdparm -tT /dev/sdb) to get a relative
> performance number between different disks (it doesn't have to be real
> specific, I just need to see percentages based on different physical
> media).
> Anyway, I noticed that if I run hdparm -tT /dev/sdb on RHEL 5.4 (2.6.18-164
> (megasas 04-08-RH2)) in an average of 10 runs I get 825MB/sec, however if I
> update the OS to 5.5 2.6.18-194.11.1 (megasas 04.17-RH1) in an average of
> 10 runs I get 561MB/sec. I am trying to figure out if this is a real
> performance decrease or if there were changes made in the new kernel or
> driver that would cause hdparm to have an issue getting the disks to work
> hard.
> If I reboot with the older kernel it is always around 825MB, I can
> reproduce this over and over.
> I will also note that in Fedora 13 it is also around 825MB/sec.
> Has anyone seen this, any thoughts?

Yes, read and write some real files to see if this is an actual drop in 
performance. hdparm is not a good benchmark.

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