Adaptec 2400A Performance

[Dan Nelson]

In the last episode (Jan 23), Rishi Chopra said:
> I've run some imperical tests on the Adaptec 2400A raid controller
> (results and setup can be seen here):
> 
> http://www.ocf.berkeley.edu/~rchopra/RaidResults.html
> 
> I was rather disappointed with the results.  Can anyone suggest what
> might be causing such slow disk speeds, or whether these speeds are
> out of the ordinary for a 4-disk FreeBSD RAID5 installation?  I have
> done nothing to configure the card aside from striping the array in
> BIOS; FreeBSD seems to automatically detect the disks.
> 
> I once ran a 2-disk RAID-0 installation on Win2k which was 6-7 times
> faster on sequential read/write tests (60-70MB/sec), hence my dismay.

RAID-5 has to do 4 I/Os for every write, which would explain the bad
write performance, but I can't explain your read performance.  It's not
strictly comparable, but a Raid-5 4x73gb SCSI setup using an Adaptec
3200S (128MB cache), which looks like it uses the same RAID engine and
firmware as your 2400A, averages 18MB/sec writes and 50MB/sec reads. 
Your card configured with a RAID 0 volume should equal your w2k speeds.
 
-- 
	Dan Nelson
	dnelson at allantgroup.com