Performance with multiple drives

[Shane Wegner <shane@cm.nu>]

Hello list,

I am experiencing a performance hit on my SCSI setup here
and am wondering if this is to be expected or whether there
is anything I can do about it.  In summary, when reading
from a single drive, I am getting read performance of
approx 73mb/s, when reading from two drives concurrently,
regardless of which two, reads drop to 64mb/sec per drive
and when reading from all three, read performance is
approximately 46mb/sec.  The drives are matched Maxtor
Atlas 10K IV sca units using a dual channel u160 onboard
aic7xxx controler.  Two drives are on channel 0 and the
third is on channel 1.  The drives are sca units so I had
to use 80/68 pin converters on all three in case that would
make a difference as I couldn't find a scsi backplane which
would support splitting the drives across the channels as
is necessary due to the 160mb/sec channel limit.

The system is a dual Pentium III tualatin setup with 1gb of
ram.  The board claims to support 64 bit 66mhz pci on the
scsi bus and I have no legacy cards on that particular bus
so it should be running at 64 bit.  However, I don't know
of a way to verify that under linux.

If anyone has any suggestions on how I can find the
bottleneck, I would appreciate it.

Best,
Shane

-- 
Shane Wegner
http://www.cm.nu/~shane/