If your seeing funny blinking lights on the drive, and you are not the only
person having problems with this particular drive model, I would be very
suspicious that a drive firmware bug is being tickled. The best solution
in this case would be to obtain a better version of the firmware from the
vendor, but lacking that you might try turning off tagged command queueing
or just reducing the number of tagged openings. I've noticed interactions
between tagged command queueing and write caching on Seagate drives, so you
might try turning off write caching and leaving the number of tagged
openings alone. You can do all this with camcontrol.
This morning I disabled write back caching in the SCSI BIOS, and the machine
has been copying files here and there for ~7 hours now with no problems at
all. As you say the performance difference is pretty much negligible.
I'm going to leave the machine copying and rm'ing files all weekend to make
sure this all is OK, but at this stage it appears disabling write caching has
fixed the problem (or at least worked around it).
Thanks very much for your help.
If this continues to work this drive/firmware combo deserves a quirk entry.