96-277r1 - Proposed Change in QErr for SPC-2

PJohansson at aol.com PJohansson at aol.com
Wed Feb 12 20:46:19 PST 1997


* From the SCSI Reflector (scsi at symbios.com), posted by:
* PJohansson at aol.com
*
Ralph et al,

Please see the comments embedded below:

In a message dated 97-02-12 16:24:14 EST, ROWEBER at acm.org writes:

<< To resolve this problem, it is proposed that the QErr bit become a two-bit
 QErr field by extending QErr to include bit position 2 in byte 3 in the
 Control mode page in SPC-2.  The text defining the QErr field will be
 constructed so that the existing meanings of QErr=0 and QErr=1 will be
 preserved, with new meanings being assigned to QErr=10 and QErr=11.  The
 following definition of the new QErr field is proposed:
 
     The queue error management (QErr) field specifies how the device server
     shall handle blocked tasks when another task receives a COMMAND
     TERMINATED or CHECK CONDITION status (see table n1).
 
 	      Table n1 - Queue error management (QErr)
 	Value	Definition
 	00b	Blocked tasks in the task set shall resume after an ACA
 		condition is cleared (see SAM).
 	01b	All the blocked tasks in the task set shall be aborted when
 		the COMMAND TERMINATED or CHECK CONDITION status is sent. 
 		A unit attention condition (see SAM) shall be generated for
 		each initiator that had blocked tasks aborted except for
 		the initiator to which the COMMAND TERMINATED or CHECK
 		CONDITION status was sent.  The device server shall set 
 		the additional sense code to COMMANDS CLEARED BY ANOTHER
 		INITIATOR.>>

What applications are expected to use the QErr value of 01b?

<< 	10b	Reserved
 	11b	Blocked tasks in the task set belonging to the initiator to
 		which a COMMAND TERMINATED or CHECK CONDITION status is
 		sent shall be aborted when the status is sent.
 
     NOTE n2 In a multi-initiator configuration, QErr=01b can produce
     looping repetitions of CHECK CONDITION status being sent to various of
     the multiple initiators or service requests being timed out because
     tasks are aborted and unit attention notification fails due to the
     absence of new service requests.
 
 It also must be noted that the proposed change in the definition of QErr
 affects the already approved proposal defining the Basic queuing model
 (96-198r4).  So that the Basic queuing model can be functional in a
 multi-initiator configuration, I propose that the previous Basic queuing
 model approval be amended to use QErr=11b and its associated definition
 above wherever 96-198r4 uses QErr=1.
  >>


It is not at all clear that this reinterpretation of QErr is in accordance
with the wishes of those who advocated (and voted for) the Basic queuing
model. I think the willingness to modify might be connected with your answer
to the question posed above.


The SBP-2 ad hoc working group is one of the significant constituencies for
the Basic queing model. We are meeting in Bothell, WA this Tuesday and
Wednesday and I will raise your concerns and suggestions tomorrow
(Wednesday).


Regards,

Peter Johansson
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