quoted

What drive configuration are you using (SCSI / ATA / SATA), what chipset

is

quoted

providing the disk interface and what cpu are you running with?

3xSATA, Seagate 320 ST3320620AS, Intel 6600, ICH7 controller using the
ata-piix driver, with drive cache set to write-back. It's not obvious to
me why that matters, but if it helps you see the problem I''m glad to
provide the info. I'm seeing ~50MB/s on the raw drive, and 3x that on
plain stripes, so I'm assuming that either the RAID-5 code is not
working well or I haven't set it up optimally.

If it had been ATA, and you had two drives as master+slave on the same
cable, then they would be fast individually but slow as a pair.

RAID-5 is higher overhead than RAID-0/RAID-1 so if your CPU was slow then
you would see some degradation from that too.

We have similar hardware here so I'll run some tests here and see what I
get...