SCSI-2 Parity Errors

Jim Kahn James.Kahn at Eng.Sun.COM
Fri Mar 17 09:30:24 PST 1995

I have seen occassional parity errors from worn cabling
(damaged that is).  I have see *HEAVY* parity errors with 
long cables and SCSI chip problems.  Otherwise, it's
fiarly rare for me.

Jim Kahn

>	From @ncrwic.WichitaKS.NCR.COM:asami at  Thu Mar 16 19:16:21 1995
>	From: asami at (Tak Asami)
>	To: scsi at
>	Subject: Re: SCSI-2 Parity Errors
>	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
>	_|/ _| WESTERN DIGITAL     (714) 932-7621 : Voice
>	_|_|_|                     (714) 932-6496 : Fax

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