Does TST == 001b break initiator software?

PJohansson PJohansson at
Sat Apr 4 18:30:29 PST 1998

* From the T10 (formerly SCSI) Reflector (t10 at, posted by:
* PJohansson <PJohansson at>
In a message dated 98-04-04 09:48:41 EST, ROWEBER at writes:

<<As for implementations using TST=001b, they are new implementations, at
least with respect to what is specified in the standards.  Since they are new
implementations, they should have no problem coping with the fact that ABORT
TASK SET is the same as CLEAR TASK SET.  Just as the standard makes it pretty
clear that a READ command will transfer data to the host, the standard can
(should) made it clear that ABORT TASK SET is the same as CLEAR TASK SET, when
TST=001b.  It's all a part of incorporating 97-225 in the draft standards.>>

This is the point that is the heart of my argument:

* If ABORT TASK SET equals CLEAR TASK SET when TST=001b, why should we have

* If the software for TST=001b is a new implementation, where is the negative
impact if CLEAR TASK SET is disallowed in this case?

* There is a finite possibility that a software implementation might misuse
CLEAR TASK SET when TST=001b and obtain incorrect target behavior (from the
viewpoint of the miscoded initiator software). If CLEAR TASK SET does not
exist when TST=001b this can never happen.

Please keep in mind that in the preceding I am *not* talking about parallel
SCSI message codes---I'm talking about SAM-2 task management services
(architectural concepts). I have never said that a parallel SCSI device that
recognizes a CLEAR TASK SET message should be noncompliant.

The area in which I am requesting a change is in the definition of CLEAR TASK
SET in SAM-2 Revision 4 which reads, at present, "This function shall be
supported by all logical units that support tagged tasks." I think this should
be amended for the TST=001b case so that support is either optional or
prohibited. My perference is for prohibited.


Peter Johansson

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