TASK SET FULL Definition(s) in FC-TAPE and SAM-2

Edward A. Gardner eag at ophidian.com
Wed Mar 17 10:30:38 PST 1999

* From the T10 Reflector (t10 at symbios.com), posted by:
* "Edward A. Gardner" <eag at ophidian.com>
George Penokie wrote:

>The is a significant difference on how an initiator is supposed to respond
>to a BUSY vs a TASK SET FULL status.
>A BUSY only tells the initiator that the command could not be received by
>the target and the initiator should try again later. There is no indication
>as to how much later from the target.
>A TASK SET FULL also tells the initiator that the command could not be
>received by the target and that in initiator should not try again until it
>receives a command complete indication from a currently outstanding
>command. So in the case of a TASK SET FULL there is an indication from the
>target as to when the initiator has a chance of having the command
>This difference is important because the way most initiators respond to
>BUSY is to immediately resend the command which has the effect of clogging
>up the SCSI bus with needless activity. Where as TASK SET FULL causes the
>initiators to hold back resending the command thus reducing traffic on the
>SCSI bus.

George, while I agree with your definitions, I cannot find any statement in
any of our standards (or proposed standards) supporting that definition of
TASK SET FULL.  For example, SAM-2 revision 9 (page 41) merely says:

TASK SET FULL. This status shall be implemented if the logical unit supports
the creation of tagged tasks (see 4.9). This status shall be returned when
the logical unit receives a command and does not have enough resources to
enter the associated task in the task set.

There is no guidance whatsoever about when or if a command should be resent,
or at least none that I can find.

The description of BUSY specifies "The recommended initiator recovery
action...".  Do you advocate adding corresponding guidance to the definition
of TASK SET FULL?  I believe I recall this subject coming up before, and
being sufficiently controversial that it was abandoned.  It would be nice if
it could finally be resolved.

Edward A. Gardner               eag at ophidian.com
Ophidian Designs                719 593-8866 voice
1262 Hofstead Terrace           719 593-8989 fax
Colorado Springs, CO  80907

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