RE: DRAFT Minneapolis Minutes -- ACA Discussion

[Black_David@emc.com]

> - SCSI ACA discussion
> 
> > ACA (Auto Contingent Allegiance) is an optional SCSI mechanism that
stops execution
> > of a sequence of dependent SCSI commands when one of them fails.  The
situation
> > surrounding it is complex - T10 specifies ACA in SAM2, and hence iSCSI
has to
> > specify it and endeavor to make sure that ACA gets implemented
sufficiently 
> > (two independent interoperable implementations) to avoid dropping ACA in
the
> > transition from Proposed Standard to Draft Standard.  On the list David
Black
> > noted that this would make ACA implementation at least a "SHOULD" rather
> > than a "MAY".
>
> Keeping in mind the underlying iSCSI issue, I assume the question here is
> not support for the ACA function as a SCSI option but whether or not iSCSI
> will MANDATE the implementation of ACA as a condition for iSCSI
compliance.

That is the current question - "SHOULD" and "MAY" refer to their
definitions in RFC 2119, and "MANDATE" would correspond to "MUST".
I apologize if this shorthand was confusing

> In that context, "dropping ACA" would amount to not requiring a logical
unit
> to implement the feature.

That's not correct because "dropping ACA" refers to a future transition of
iSCSI
from Proposed Standard to Draft Standard status.  As part of that
transition,
any feature without two independently developed interoperable
implementations
is removed from the RFC as part of revising it for Draft Standard.  The
feature
isn't just made optional - the text describing such a feature is deleted.
The WG
has a fair amount of control over when the transition occurs, but the
transition
should be a goal, as the resulting cleansing of unimplemented features from
the specification is usually a good thing.  In ACA's case, its removal would
not be a good thing since it would cause iSCSI to no longer be a complete
SCSI transport mapping, and hence it behooves us to word the specification
now to encourage ACA to be implemented.

As I said, this situation is complex - I hope this explanation is clearer.

--David
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