freebsd, adaptec aic7902, 4 or more seagate drives == resets

[Don Bowman]

has anyone successfully used 4 or more seagate
[10K or 15K] U320 drives on a single scsi
bus with an adaptec aic7902 controller?

I have found that with the 7902 [ahd], i get
repeated scsi bus resets [time outs]. With
an adaptec 2200s controller [which also uses
the 7902], i get the same behaviour.

The other drives don't need to be active, just
booting from one with the other 3 quiescent
on the bus is sufficient.

The error usually occurs as the os is coming up,
you see the banner of SCB timed out, reset [when
using AHD], or a scsi bus reset message [aac].

the 10K drive is using seagate firmware 007,
the 15K is using seagate firmware 006.
[as per http://www.seagate.com/support/disc/u320_firmware.html]

The AAC kept resetting the bus when in its bios
trying to rebuild the raid, so i'm guessing
its not a driver issue.

I'm sure this is not terminator, electrical, power,
cable, etc., they have all been swapped, checked,
etc. Multiple systems have been tried. Backplanes
versus cables have been tried.

--don