OT: FC4+Poweredge 850+Perc 4/sc = slow disk performance

[Mike McMullen]

Hi All,

I am setting up a Dell PowerEdge 850 with FC4 (customer's app requires it).

It has 2GB of RAM, 3.2GHZ Pentium 4 and a PERC 4/SC (aka megaraid)
raid controller with two seagate SCSI-3 300GB 10,000RPM drives.

I have configured the logical drive as RAID 1 (mirroring) with the defaults for
for a logical drive 0 - StripeSize 64K, Write Policy = Write Through, Read
Policy = Adaptive, Cache Policy = DirectIO.

I have a 250GB partition (per customer's request). When I run
hdparm -t -T on the device I get ~2408MB/sec on cached reads.

On buffered disk reads I get ~35MB/sec which seems awfully slow
given the h/w. I'm running the system in single user mode to eliminate
background processes. 

My buffered reads will start at 50MB/sec and after ~8-10 iterations drops
to ~35 MB/sec.

For a test I installed FC5 and there buffered reads were around ~75MB to
start with and after ~8-10 iterations dropped to ~39MB/sec.

Can anyone shed any light on why the i/o appears so slow? On 7500 RPM
SATA with drives I get buffered reads of around ~60-70MB.

I've tried changing parameters in the PERC controller screen but nothing seems
to work.

Any insight appreciated!

Mike