libata + SATA + aacraid == bad performance?

[kristian.hermansen at gmail.com (Kristian Hermansen)]

In kernel 2.6.17 on Ubuntu I was seeing an average of 107 MB/s read
speed from hdparm -t with a software RAID0 array containing two
identical large SATA drives.  This speed was about 60 MB/s for each
drive individually.

However, now with 2.6.17 and an actual Adaptec hardware raid
controller utilizing a RAID0 array on four of these identical large
drives, we are only seeing about 120 MB/s.  I would have thought this
number should jump significantly given double the drives in the array
(2->4).  One other problem is that hdparm is now reporting
"HDIO_DRIVE_CMD(null) (wait for flush complete) failed: Inappropriate
ioctl for device", but I am told this is a small error that can be
ignored since the aacraid driver is trying to wait for a flush to
occur, but that the new libata subsystem (since 2.6.15?) is causing
that to fail.

I would ideally like to see 200 MB/s read speed here.  Any suggestions
on the poor read performance?
-- 
Kristian Hermansen

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