SCSI-2 Parity Errors

Lawrence Chen lchen at pyramid.com
Wed Mar 15 11:39:30 PST 1995


On Mar 15, 10:32am, Denis Brockus wrote:
> Subject: SCSI-2 Parity Errors
> I am having a hard time determining what to do from a target point of view
> when I detect a parity error. I know that a target should not reply to a
> selection if there is a parity error in the SELECTION phase.
> 
> When the target is in MESSAGE OUT phase, there are two options after
> retries have been exhausted:
>     1)	return CHECK CONDITION status and set the sense key to ABORTED
> 	COMMAND and the additional sense code to MESSAGE ERROR.
>     2)	indicate an exception condition by performing an unexpected
> 	disconnect. (? what happens to the I/O process? is it aborted?)
> 
> What should happen if parity errors are detected in COMMAND and/or DATA OUT
> phase? How should retries be performed in each of these situations and
> what should happen after retries have been exhausted?
> 
> Thanks, Denis

Hi Denis,

As a suggestion, Zadian's Host Basher software is quite helpful in
learning the details of error recovery.

In general, a target device has three options as you mentioned when a
parity error is detected:
1) retry
2) check condition
3) disconnect

for data phases, the target must remember to reset the host's current 
data pointer before data phases are retried.

-Larry

> -- 
> 
>       _/_/_/_/    _/_/_/_/            | Denis Brockus
>      _/     _/   _/     _/            | denis at arraytech.com
>     _/     _/   _/     _/             |
>    _/     _/   _/_/_/_/               | Array Technology
>   _/     _/   _/     _/               | 4775 Walnut Street, Suite B
>  _/     _/   _/     _/                | Boulder, Colorado 80301
> _/_/_/_/    _/_/_/_/                  | Tel(303)938-6057  Fax(303)444-0059
>-- End of excerpt from Denis Brockus



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