PERC 320/DC in Precision 650 with RHEL5; Pitiful Disk Performance

J. Epperson Dell at
Wed Sep 30 18:23:01 CDT 2009

On Wed, September 30, 2009 18:55, Charles Knox wrote:
> Hi all, For reasons of application compatibility I have recently upgraded
> a Precision 650 from RedHat 9 (which it shipped with) to RHEL5.  The disk
>  system in this machine is four 143GB SCSI drives as a RAID5 set on the
> PERC320/DC Adaptec built controller.  Before the update, the performance
> of the RAID was sort-of OK, no great shakes but I suspect it would do
> Read/Write operation at about 40MB/sec.  Since the update performance has
>  taken a BIG hit.  At first I could get only about 3 MB/sec on the RAID
> with the load on the system going up into the over 12 regime.  A web
> search on the aacraid driver plus performance yielded a hit at the SuSE
> site having to do with telling the driver to not do write caching with a
> modification to /etc/modprobe.conf; adding the line
> options aacraid cache=2
> I did this, and performance screamed up to 5-6MB/sec, but the load still
> skyrocketed when large writes were done.  Does anyone have any ideas
> about how to speed this up, aside from launching the PERC out the window
> and attaching the disks to the LSI controller in the system and trying
> software RAID?

Have not touched a  320 in a long time, but IIRC there's a background
consistency check option somewhere that if turned on will really bog down
a RAID 5.  Look for that.

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