SCSI-2 Parity Errors

Tak Asami asami at dt.wdc.com
Thu Mar 16 19:07:09 PST 1995


I usually don't respond to discussion like this, but this is too exciting
to pass up.... Here's my two cents.

Have anyone ever seen in this life an "occasional" occurance of SCSI parity
error?  In my limited experience, it either never happens or happens ALL THE
TIME.  In other words, all parity errors I've seen are hard errors.

Where do parity errors come from?  Intermittent cable/connector connection,
cold solder joints on your Heathkit SCSI drive, disintegrating PC board trace,
a dead device on the bus (OJ did it!).
This is definitely a different animal from bit error rate on magnetic record-
ing read-write!

My immediate reaction to SCSI parity error is that the bus must be suffering 
a catastrophic failure.  And any transfer across the bus is deemed unreliable.
Forget the message, forget the sense data.  You can't use it.
Forget the tricky error recovery.

The best policy in my mind is like Jim Mcgrath says, abort everything and
start over. It doesn't take that long.  And for a "working" system, you'll
never have to do it, anyway.


=========================================================================
                           Tak Asami
_|_|_|                     asami at dt.wdc.com
_|/ _| WESTERN DIGITAL     (714) 932-7621 : Voice
_|_|_|                     (714) 932-6496 : Fax





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