Re: [storm] WG Last Call comments on consolidated iSCSI draft

I agree - second try at text:

OLD
  ACA helps preserve ordered command execution in the presence of
  errors. As iSCSI can have many commands in-flight between
  initiator and target, iSCSI initiators and targets SHOULD support
  ACA.
NEW
  Some SCSI initiators use ACA to enforce ordered command execution
  during error recovery, and hence iSCSI initiator implementations
  for those SCSI initiators need to support ACA.  In order to support
  error recovery for these SCSI and iSCSI initiators, iSCSI targets
  SHOULD support ACA.

As Ralph noted, an implementer of an iSCSI initiator that needs ACA will know
it, or learn quickly when error recovery doesn't work right wrt the SCSI class
driver :-), so the primary purpose of the SHOULD in this text is to tell
target implementers about the need for ACA support.

FWIW, this is a "SHOULD" and not a "MUST" because a target implementer may
choose not to support initiators that use ACA - that absence of ACA support
will be detected quickly at the SCSI level, as the first SCSI command that
sets the NACA bit in the CONTROL byte in the CDB will get hit with a
CHECK CONDITION for having done so.

Thanks,
--David

> -----Original Message-----
> From: storm-bounces@ietf.org [mailto:storm-bounces@ietf.org] On Behalf Of Julian Satran
> Sent: Sunday, August 28, 2011 1:15 AM
> To: Ralph Weber
> Cc: storm@ietf.org
> Subject: Re: [storm] WG Last Call comments on consolidated iSCSI draft
> 
> Ralph,
> 
> I think you caught a nit. Your point is correct - WRT initiators.
> The SHOULD statement should refer to targets only.  Initiators that are not supporting ACA may have a
> hard time surviving in the same environment with initiators that require and support ACA  but will
> cause no harm to those that require and support it.
> 
> Julo
> On Aug 28, 2011, at 5:18 AM, Ralph Weber wrote:
> 
> > I am having a little bit of difficulty following the logic of the
> > proposed new text.
> >
> > First it says that some initiator implementations use ACA (which
> > implies that some do not). Then, it says that iSCSI initiators
> > (presumably all iSCSI initiators) ... SHOULD support ACA.
> >
> > I can understand why initiators that need ACA SHOULD support it,
> > but why should the others bear the burden?
> >
> > All the best,
> >
> > .Ralph
> >
> > On 8/27/2011 5:36 PM, david.black@emc.com wrote:
> >> <WG chair hat off>
> >>
> >> In that case, let's at least get the explanation for the SHOULD right ;-).
> >>
> >> Here's a suggestion ...
> >>
> >> OLD
> >>   ACA helps preserve ordered command execution in the presence of
> >>   errors. As iSCSI can have many commands in-flight between
> >>   initiator and target, iSCSI initiators and targets SHOULD support
> >>   ACA.
> >> NEW
> >>   Some SCSI initiator implementations use ACA to enforce ordered
> >>   command execution during recovery from errors.  In order to support
> >>   error recovery in such SCSI initiators, iSCSI initiators and targets
> >>   SHOULD support ACA.
> >>
> >> Thanks,
> >> --David
> >>
> >>> -----Original Message-----
> >>> From: Knight, Frederick [mailto:Frederick.Knight@netapp.com]
> >>> Sent: Friday, August 26, 2011 8:51 AM
> >>> To: Black, David
> >>> Cc: storm@ietf.org
> >>> Subject: RE: [storm] WG Last Call comments on consolidated iSCSI draft
> >>>
> >>> I disagree.
> >>>
> >>> 1) while not common, the hosts that use it, do need it;
> >>> 2) the original 3720 text contains a SHOULD; and
> >>> 3) there is no good reason for us to be weakening this statement.
> >>>
> >>> 	Fred Knight
> >>> 	NetApp
> >>>
> >>> -----Original Message-----
> >>> From: david.black@emc.com [mailto:david.black@emc.com]
> >>> Sent: Thursday, August 25, 2011 5:55 PM
> >>> To: storm@ietf.org
> >>> Subject: [storm] WG Last Call comments on consolidated iSCSI draft
> >>>
> >>> <...text removed...>
> >>>
> >>> [D] Section 10.2 contains a "SHOULD" requirement for ACA
> >>> (Auto-Contingent Allegiance) support.
> >>> As ACA support in SCSI initiators is not common, I suggest weakening
> >>> this to a MAY requirement.
> >>>
> >>>
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> >>
> >>
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