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

Charles Knox knox at
Wed Sep 30 17:55:18 CDT 2009

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

Charley Knox
Department of Astronomy
Case Western Reserve University

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