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
> 

Also the kernel driver being used is megaraid_mbox.

Mike