SAM requirements for ACA on unsupported logical unit?

[Stephen Byan]

* From the T10 Reflector (t10 at t10.org), posted by:
* Stephen Byan <Stephen.Byan at quantum.com>
*
Hi all,

I'm looking for some clarification on the SCSI-3 Architectural Model (SAM)
requirements on auto contingent allegiance behavior for unsupported logical
units. As I read the standard, it calls for:

1) BUSY, RESERVATION CONFLICT, ACA ACTIVE, or TASK SET FULL take precedence
over other status conditions. (clause 5.2)

2) a command returning CHECK CONDITION status causes an auto contingent
allegiance (ACA) condition. (clause 5.6.1)

3) if a faulting command has the NACA bit set, the ACA condition is only
cleared by a power on, hard reset, or CLEAR ACA task management function.
(clause 5.6.1.2)

4) a target shall respond to a command other than INQUIRY or REQUEST SENSE
to an unsupported logical unit by returning CHECK CONDITION. (clause 5.6.3,
subpart a)

Taken together, these imply that an auto contingent allegiance condition
shall exist for the addressed logical unit after a target receives a command
addressed to an unsupported logical unit.


I haven't read SAM-2 in detail, but it seems to have the same wording, so I
think it has the same problem.


I'm assuming the correct thing to do is to not establish an ACA, and to
simply follow the rules in clause 5.6.3. In other words, in the following
sequence:

a) Initiator A sends READ command to unsupported logical unit X.
b) Initiator B sends READ command to unsupported logical unit X.
c) Initiator A sends REQUEST SENSE command to unsupported logical unit X.

initiator B should receive CHECK CONDITION status in step c), not ACA
ACTIVE, 
and in this sequence: 

a) Initiator A sends READ command with Normal ACA set to one to unsupported
logical unit X.
b) Initiator A sends READ command without ACA attribute to unsupported
logical unit X.
Note there is no intervening CLEAR ACA function between steps a) and b). 

initiator A should receive CHECK CONDITION status in step b), not ACA
ACTIVE.


Have I missed something, or does the spec need clarification to state that
an ACA shall not be established for an unsupported or unattached logical
unit? (Or alternatively that CHECK CONDITION shall take precedence over
other status for unsupported or unattached logical units.)

Thanks in advance.

Regards,
-Steve


Steve Byan <stephen.byan at quantum.com>
Design Engineer 
Quantum Corporation <http://www.quantum.com>
MS 1-3/E23
333 South Street
Shrewsbury, MA 01545
voice: (508) 770-3414 
fax: (508) 770-2604
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