X3T9.2/93-064R0

To:        Membership of X3T9.2

From:      Ralph O. Weber
           Digital Equipment Corporation

Date:      March 30, 1993

Subject:   Disposition of ASC/ASCQ tag number in X3T9.2/92-141R5


The Tagged Queuing proposal approved at the October '92 Plenary
(92-141R5) includes a new ASC/ASCQ for reporting duplicate tag
usage.  The ASC is 4Dh and the ASCQ byte identifies the duplicate
tag value.  Usage of a byte for this information conflicts with
the 64-bit field defined for tag values by the SCSI-3 Archi-
tecture Model (SAM).  This document describes some options for
dealing with this conflict.

Option one is adding a 64-bit tag field to the REQUEST SENSE
data.  I assume that the new field would be used for all types
of error reports.  Thus, the tag associated with the problem
condition would always be available (instead of available only
during duplicate tag conditions).

Another option is dropping the duplicate tag data entirely.  One
can argue that, if an initiator can successfully retrieve REQUEST
SENSE data, then the value of the duplicate tag is already known. 
If this option is chosen, I propose use ASC/ASCQ 4E 01 to repre-
sent OVERLAPPED TAGGED COMMANDS.  This leaves all of ASC/ASCQ
4D NN available for future standardization.