Definition of Mandatory

Jim McGrath jmcgrath at qntm.com
Fri Sep 9 15:36:40 PDT 1994


        Reply to:   RE>>Definition of Mandatory 


> That's an issue to be addressed by protocol standards and implementations.
The 
> point is that SAM requires the system, as seen by an application client
looking 
> through the service delivery port, to behave in a certain way, in this case
as 
> though the task set resides in the logical unit.SAM then delegates the 
> responsibility for correctly defining the corresponding enforceable
behavior to 
> the protocol standards. SAM is the reference we use to decide whether or
not a 
> given protocol complies with SCSI-3.

>>At the end of the day, I am still concerned over possible confusion between
>>things SAM requires of standards and things it requires of implementations.
>>And since it is not focused on specific implementations, it is very hard
>>for it to make implementation requirements in a manner that is clear and
>>enforceable to the designer of a specific device.

>It would help if you were to cite examples of requirements you feel might be
a 
>potential source of confusion. In my opinion, it's the job of the 
>implementation standards and SAM to cooperatively address such issues on a
case 
>by case basis..

As a sepecific example, the whole task set issue can be cited.  If it is
really
part of the "standards for standards" stuff in SAM, that is not clear. 
Moreover,
none of the protocol documents existing or planned elaborate on queuing
to any greater degree at, say, the specific device level.  There is a gap
there.  While one can argue where it should go, I thought one of the initial
goals of SAM was to incorporate on this point all the device specific
requirements
originally in the SCSI-3 queueing paper.

My problem is that if I have a question about queuing, it is unacceptable for
SCSI-3 to say that it can be implemented in either the host or the target -
that ducks the issue, and makes practical hash out of SCSI.  Since people
seem
to feel that SAM covers queuing, then it has to address these issues at that
level.  But I still feel very uncomfortable with all that stuff (even if it
did
exist today) being in an architecture document - how are we going to document
Parallel, Fibre, SSA, SBP queuing issues all in the degree needed in SAM?

Another trivial example is LUN space.  We have a very large space defined
in SAM - do I have to support that on the device?  Clearly I will not, but
it is not clear to me how people would interpret SAM if we are
confusing over that standards for standards and implementation issues.
And your original wording seemed to imply that I would be required to
support that stuff at the device level.

Jim






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