Disk performance drop in new RHEL 5 kernel?

Drew Weaver drew.weaver at thenap.com
Thu Aug 26 13:05:45 CDT 2010

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?


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