Slow transfer speeds with U320 drives and HP Smart Array 641

[Nelis Lamprecht]

Hi,

I posted this to freebsd-hardware but haven't received a response so thought I'd
try this list. Please excuse the cross-posting.

With the ciss driver on my HP ProLiant ML350 I've noticed the transfer
speed on my RAID controller is only 135.168MB/s.

da0 at ciss0 bus 0 target 0 lun 0
da0: <COMPAQ RAID 1  VOLUME OK> Fixed Direct Access SCSI-0 device
da0: 135.168MB/s transfers
da0: 69459MB (142253280 512 byte sectors: 255H 32S/T 17433C)

Both my drives on the RAID controller are U320 72GB pluggable SCSI's.
The RAID card has the optional 64MB battery backed cache enabler installed.
I also have a AIC 50/100 Tape Drive in the machine which is connected to the
onboard SCSI interface.

ahc0: <Adaptec (Compaq OEM) 3960D Ultra160 SCSI adapter> 
aic7899: Ultra160 Wide Channel A, SCSI Id=7, 32/253 SCBs
ahc1: <Adaptec (Compaq OEM) 3960D Ultra160 SCSI adapter> 
aic7899: Ultra160 Wide Channel B, SCSI Id=7, 32/253 SCBs

sa0 at ahc1 bus 0 target 6 lun 0
sa0: <COMPAQ SDX-500C 1.35> Removable Sequential Access SCSI-2 device
sa0: 40.000MB/s transfers (20.000MHz, offset 7, 16bit)

My question is why the slow transfer speed of the RAID controller ? Does this
have anything to do with the slower SCSI Tape Drive/U160 channels or is this a 
limitation of the ciss driver ? The U320 drives are not in any way connected to
the slower drive so it shouldn't effect the speed or should it ?

Hopefully someone here has a similar system and can offer me some insight. 
Thanks for your reply.

Kind Regards,
Nelis