96-274r0 -- Proposed Change in QErr=1 Behavior for SPC-2

Gerry Houlder Gerry_Houlder at notes.seagate.com
Thu Nov 21 13:10:56 PST 1996


* From the SCSI Reflector (scsi at symbios.com), posted by:
* Gerry Houlder <Gerry_Houlder at notes.seagate.com>
*
Quoting Ralph's message:

>This proposal solves the problem by eliminating the interaction between 
>a CHECK CONDITION status sent to one initiator and the handling of tasks
>belonging to other initiators.  This proposal also can be viewed as
>reducing implementation complexity in the device server.

(1) This proposal doesn't reduce the implementation complexity in the device
server. It requires the device server to test each command to see which
initiator it is from and then choose to either abort it or maintain it. This is
MUCH more difficult that aborting everything unconditionally. 

(2) He is actually trying to reduce the initiator complexity, not the device
server complexity. The fact is that the QErr feature was designed for
single initiator systems and multi-initiator systems were supposed to use
the ACA ACTIVE technique (or at least normal contingent allegiance) so
commands from other initiators weren't blown away. This is more work for
the initiator to conditionally decide which other commands it has sent
should be aborted because of the failed command. He just wants to
push the hard work down to the device instead of doing it himself !!

(3) This flies against the "simple queuing" proposal presented by Peter
Johanson, based on an earlier proposal by Jim McGrath. That proposal
unequivically stated that it is more difficult to do "conditional aborts".
This is why ABORT TASK and ABORT (where only one initiator's commands
are aborted) were removed from the simple queuing set.

(4) This proposal also affects Charles Monia's proposal to add an "ACA
like" behavior for RESERVATION CONFLICT, QUEUE FULL, etc. Perhaps
Ralph should support Charles' proposal and use that technique instead of
changing an older feature.

Just for the record, I don't like this change. Ralph is messing with a feature
whose behavior has been well defined for many years and is liked by a
lot of customers JUST THE WAY IT IS.
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