"Timothy E. Denehy" writes:
> 
> The four disks are Seagate ST318305LC, and there are two Adaptec 39160
> controllers, with two disks attached to each.  The machine is a Dell
> PowerEdge 4400.
> 
> I've been able to achieve 80 MB/s sequential writes by manually striping
> across the four disks with a test program, but combining them into a RAID
> array greatly reduces the throughput.

This sounds like the "drive doesn't do very well when RAIDframe only hands it 
a few KB of data for each IO" problem.  For kicks, turn on the write-back 
cache (I'm betting it's off) and see how the disks do.. (You can turn it on 
via the 39160 BIOS, IIRC)  If it does the full 80MB/sec, then it's probably 
the way RAIDframe is handing the data off to the drives in 
little bitty chunks...  Check the various archives -- the problem has
been discussed on the NetBSD lists before...  Whether you leave the 
write-back cache on is up to you, but it might help clarify what's going 
on.....

Later...

Greg Oster