I've seen hard lockups on three rather different machines that seem to
be due to problems with the adaptec driver. One machine is a PPro-200
with Intel mainboard, the other two are a P166, Gigabyte mainbord w/HX
chipset AFAIR. On all three machines the lockup could be triggered by
simply copying large files (abt 3-5Meg each) from CDROM to one of the
SCSI disks. The machines lock up hard, nothing in the logs.
For one of the machines (my own one) I solved the problem by replacing
the 2940U with an older non-ultra-2940 controller. None of the three
machines is equipped with Ultra-SCSI devices, though.
Last night I compiled a kernel with tagged command queueing disabled and
the particular machine, one of the P166, is up since then and has not
shown any unusual behaviour. However, this machine has been running the
July-27 snapshot of the driver with tagged command queueing enabled
without problems.
The lockups happen on no-load conditions, too. On the PPro it once
happended on simply mounting the CDROM. Compiling the Kernel has been
successful in any case, however.
To gather some more information I'll try to redirect kernel messages to
the console on one of the P166, the PPro is a production machine and now
back at 2.0.26
-- Matthias