Unit attention after block descriptor

Gerry.Houlder at seagate.com Gerry.Houlder at seagate.com
Tue Jun 12 08:52:47 PDT 2001


* From the T10 Reflector (t10 at t10.org), posted by:
* Gerry.Houlder at seagate.com
*

In my view (and I think the view for the follow on SAM, SPC, SPI standards)
your "understanding 2" should be the overriding behavior. This is my
reasoning:

a) The committee has long been of the opinion that Unit Attentions that
simply report an event that the initiator asked for are redundant. This is
why the general rule of "mode parameter changed by another initiator" is
expressed. The initiator that performed the change should already know the
change occurred, so doesn't need to have a unit attention.

b) There is also a concept of a device saving mode parameters on a per
initiator basis. In this case, one initiator changing such a parameter will
not create any unit attentions for other initiator because their parameter
hasn't changed. For the case of the block descriptor, however, it is not
possible to have separate parameters on a per initator basis. Remember that
these parameters are the logical block size and capacity of the logical
unit. I think the first set of words from SCSI-2 were simply trying to
emphasize that point.

c) Note that your "understanding 1" is based on making assumptions about
the meaning of the phrase "a unit attention (see 7.9) shall be generated
when any block descriptor values are changed". Your assumption is that all
initiators always change (ignoring the see 7.9 reference). My assumption is
that you have to see 7.9 to get the full details of how a unit attention
should be created for this situation. This might be more clear if the
original sentence was "a unit attention shall be generated as described in
7.9 whan any block descriptor values are changed".





"Alan Dayley" <adayley at adtron.com>@t10.org on 06/07/2001 04:52:10 PM

Sent by:  owner-t10 at t10.org


To:   t10 at t10.org
cc:

Subject:  Unit attention after block descriptor


* From the T10 Reflector (t10 at t10.org), posted by:
* Alan Dayley <adayley at adtron.com>
*

I need clarified two parts of the SCSI-2 specification.

Section "8.3.3 Mode parameters", paragraph right after "Table 93 - Mode
parameter block descriptor", the last sentence states:

"A unit attention condition (see 7.9) shall be generated when any block
descriptor values are changed."

UNDERSTANDING 1: To me this means "Generate a unit attention when block
descriptor values are changed. Always. For all initiators. All of them."

Section "7.9 Unit attention condition" describes the events which generate
a unit attention condition.  Event "b)" states:

"b) The mode paramters in effect for this initiator have been changed by
another initiator;"

Note the terms "this initiator" and "another initiator."

UNDERSTANDING 2: To me this means "Generate a unit attention for initiator
A (this initiator) if initiator B (another initiator) changed the mode
paramters.  Initiator B does not need a unit attention because he made the
change."

Assuming UNDERSTANDING 2 is correct, that would mean that in a one
initiator, one target system a unit attention does NOT need to be generated
when the one initiator changes mode parameters.  But that violates
UNDERSTANDING 1 that mode parameter changes always generate unit attention
for all initiators.

So, finally, my question: is UNDERSTANDING 1 correct or UNDERSTANDING 2
correct or am I not UNDERSTANDING?  ;^)

Alan

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