Re: [storm] iSCSI version descriptors (for SCSI SPC-4)

Mallikarjun Chadalapaka <cbm@chadalapaka.com> Wed, 22 September 2010 19:48 UTC

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Subject: Re: [storm] iSCSI version descriptors (for SCSI SPC-4)
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Hi David,

Thanks for circling back to this.

Your outline looks good overall, I like the proposed ability to let the
relevant IETF WG choose the iSCSI version descriptors and associated
semantics - based on a "pre-approved" numbering space from T10, albeit the
"pre-approval" might in fact happen at the end as you say once we have the
RFC numbers and an established IANA registry.

I have two specific comments:

1) To be safe, I think we need one more defined value for
iSCSIProtocolLevel:
	0: No version claimed (legacy implementations)
	1: RFC 3720+RFC 5048 (iSCSI protocol, with corrections and
clarifications)
	2: RFC-iSCSI-consolidated (with obsoleted markers & auth mechanisms
and all other tweaks relative to previous baseline)
	3: RFC-SAM-4 (with SAM-4 compliance support)

2) If the above looks reasonable, particularly the ordering (with implied
superset semantics), seems to me that the iSCSIProtocolLevel key definition
has to be in the RFC-iSCSI-consolidated for it to be able to claim a smaller
number (as smaller numbers indicate chronological predecessors).

Thanks.

Mallikarjun

> -----Original Message-----
> From: david.black@emc.com [mailto:david.black@emc.com]
> Sent: Monday, September 20, 2010 8:46 AM
> To: cbm@chadalapaka.com; Frederick.Knight@netapp.com; storm@ietf.org
> Cc: david.black@emc.com
> Subject: iSCSI version descriptors (for SCSI SPC-4)
> 
> It's time to come back to this topic.
> 
> I believe that what should happen is to have SPC-4 point to an IANA
registry for
> all iSCSI version descriptors other than the existing "(no version
claimed)"
> descriptor (might be SPC-5 by the time we get all the pieces in place).
The
> reason for doing this is to put IETF in a position to create new version
> descriptors for iSCSI without having to ask T10 to do so (although, it
makes
> sense to ask T10 to reflect the currently-valid version descriptors for
iSCSI in
> each version of SPC).
> 
> Getting this to happen requires some work.  For starters, note that the
existing
> 0x960 iSCSI version descriptor can be used by any version of iSCSI - "no
version
> claimed" means that no assumptions can be made about presence or absence
of
> functionality.  For that reason, my personal (not as WG chair) preference
is that
> we create a version descriptor for RFC 3720 + RFC 5048 as reflected in the
new
> combined iSCSI draft, in order to provide a means for an implementation to
> promise support for the corrections and clarifications in RFC 5048 - that
> descriptor should also promise support for NAA iSCSI names (RFC 3980) and
the
> Node Architecture key (RFC 4850).  Not using any iSCSI version descriptor,
or
> using the existing 0x960 version descriptor, doesn't declare absence of
support -
> the only valid inference that an application client (initiator) can make
is "don't
> know".  We do need to get to a conclusion on whether to define this
version
> descriptor.
> 
> The actual mechanics for coordinating this across IETF and T10 involve
several
> steps:
> (1) The "iSCSIProtocolLevel" key should be defined in the consolidated
iSCSI
> draft, including creation of an IANA registry for its values (range: 0 -
31) and
> defining the first two values:
> 	0 - unknown (equivalent to a NotUnderstood response to the key)
> 	1 - 3720 + 5048, etc., as reflected in the consolidated iSCSI draft.
> I included 0 for completeness - it's not strictly necessary.  This moves
creation of
> that key from the SAM 4/5 features update draft to the main consolidated
draft
> (2) The new SAM-4/5 features draft then defines the value 2 and adds it to
that
> IANA registry.
> (3) As an interim measure, after WG last call is completed, we (that
probably
> means Fred and I) write a T10 proposal to create the version descriptors
0x961
> and 0x962 (corresponding to the values 1 and 2 for the
"iSCSIProtocolLevel"
> key).  That makes both version descriptors usable, and provides an
opportunity
> for the (inevitable) T10 input on exactly how the values of the
> "iSCSIProtocolLevel" key are specified.
> (4) After the RFCs are published for both drafts (yes, I'm an optimist),
another
> T10 proposal then updates SPC-4 to cross-reference the IANA registry.
> 
> Combining steps (3) and (4) at T10 would require both early creation of
the IANA
> registry and early assignment of the RFC numbers.  It's not immediately
clear to
> me that this should be done - we can figure out whether/how to do this at
the
> time when the first T10 proposal needs to be written.
> 
> Comments?
> 
> Thanks,
> --David
> 
> 
> > -----Original Message-----
> > From: Mallikarjun Chadalapaka [mailto:cbm@chadalapaka.com]
> > Sent: Monday, March 08, 2010 2:06 AM
> > To: 'Knight, Frederick'; Black, David; storm@ietf.org
> > Subject: RE: [storm] SCSI Version Descriptors - iSCSI and SAM-5
> >
> > Agreed on the SAM-5 version descriptor.  I assume the new draft will
> > in addition reference SAM-4.
> >
> > On the iSCSI version descriptions, I actually think creating a
> > 3720+5048 version descriptor is a good start.  As Fred says, existing
> > implementations will be initially not reporting this so the initiator
> > is left to other means to figure out the compliance level (and iSCSI
> > provides the hooks to discern that).  However, I believe this new
> > version descriptor will help provide clarity down the road as existing
> > implementations catch up to the standard - as opposed to leaving it
> > open-ended until all implementations catch up to the SAM-5 draft (which
takes
> even longer to get to).
> >
> > So I guess my preference is to create a 3720+5048 version descriptor,
> > assuming it's OK to approach T10 any time in future with a request to
> > add additional milestones based on implementation feedback from the WG.
> >
> > Thanks.
> >
> > Mallikarjun
> >
> >
> >
> > > -----Original Message-----
> > > From: storm-bounces@ietf.org [mailto:storm-bounces@ietf.org] On
> > > Behalf Of Knight, Frederick
> > > Sent: Tuesday, March 02, 2010 10:20 AM
> > > To: Black_David@emc.com; storm@ietf.org
> > > Subject: Re: [storm] SCSI Version Descriptors - iSCSI and SAM-5
> > >
> > > I agree, we need to request a frozen SAM-5 version descriptor, and
> > > see what they say.
> > >
> > > I'm reluctant to create a new descriptor to indicate compliance with
> > > something old (3720+5048).
> > >
> > > All those existing implementations that support 3720+5048 will NOT
> > > have that descriptor.  What is an initiator to think?  How will the
> > > initiator tell an old compliant device that supports 3720+5048 with
> > > no descriptor from the new compliant device that supports 3720+5048
> > > but has the descriptor?  My fear is a host that assumes that if the
> > > 3720+5048 descriptor you propose is NOT present, then the device must
> NOT be 3720+5048 compliant.
> > >
> > > I'm reluctant to punish existing compliant devices by creating a
> > > descriptor that they will not report.  The horse is already out of
> > > the barn, what good will it do to post a "please close the door" sign?
> > >
> > > We should however, request that T10 create a descriptor that
> > > indicates compliance with the new SAM features draft (which
> > > therefore means
> > > 3720+5048+xxx; where xxx=the new SAM features RFC).  If the device
> > > 3720+5048+doesn't
> > > report this new descriptor, then you must use iSCSI mechanisms to
> > > determine if the device is 3720 only, or 3720+5048.
> > >
> > > 	Fred Knight
> > >
> > > -----Original Message-----
> > > From: Black_David@emc.com [mailto:Black_David@emc.com]
> > > Sent: Monday, March 01, 2010 5:53 PM
> > > To: storm@ietf.org
> > > Subject: [storm] SCSI Version Descriptors - iSCSI and SAM-5
> > >
> > > <WG Chair Hat On>
> > >
> > > We have some interesting technical decisions to make around asking
> > > for some SCSI version descriptor values.  For those not familiar
> > > with them, a SCSI device can return up to 8 2-byte version
> > > descriptors in bytes 58-73 of standard INQUIRY data (see section
> > > 6.4.2 in SPC-3 or the latest draft of SPC- 4).  A version descriptor
value
> specifies both a standard and a revision.
> > > Version descriptor values are defined by explicit action at T10;
> > > this serves as an indirect control over which versions of standards
> > > to which a device can claim to comply, and discourages compliance
> > > with revisions that are unstable or otherwise unsuitable.  T10 only
> > > assigns version descriptors to drafts of standards that T10 believes
to be
> stable (e.g., suitable to implement from).
> > >
> > > The straightforward decision is that the iSCSI features update draft
> > > (draft-
> > > ietf-storm-iscsi-sam) will need to reference a stable version of the
> > > SAM-5 standard (under development) prior to the completion of SAM-5
work
> at T10.
> > I
> > > suggest that Fred Knight (editor of the draft) and I discuss this at
> > > next week's meeting of T10 (specifically, the CAP WG in T10) in a
> > > couple of weeks and bring the resulting recommendation to the storm
> > > WG list and the Anaheim meeting.  Based on what's in the current
> > > draft of SAM-5, T10 may assign a version descriptor, or recommend
> > > that we wait for some more things that are known to be inbound.
> > >
> > > The more interesting decision is version descriptors for iSCSI.
> > > Currently, there's only a generic version descriptor value , 0x960h
> > > "iSCSI (no version claimed)".  There are an additional 31 descriptor
> > > values available to iSCSI, and so the question to the storm WG is -
what
> would we like to see defined?
> > >
> > > I have two initial suggestions:
> > > 1) I suggest asking that a version descriptor be defined for the
combination
> > > 	of RFC 3720 (iSCSI) and RFC 5048 (iSCSI corrections and
clarifications)
> > > 	to enable a device to claim that it has implemented RFC 5048.  We
could
> > > 	add additional RFCs to this set, e.g., RFC 3980 for NAA names,
although
> > > 	I'm not sure that's useful to know post-login.'
> > > 2) I strongly suggest *not* asking that a version descriptor be
defined
> > > 	for RFC 3720 by itself, as I'm concerned that such a descriptor
would
> > > 	serve as a (small) disincentive to implement RFC 5048.
> > > Please comment on these.
> > >
> > > Thanks,
> > > --David
> > > ----------------------------------------------------
> > > David L. Black, Distinguished Engineer EMC Corporation, 176 South
> > > St., Hopkinton, MA  01748
> > > +1 (508) 293-7953             FAX: +1 (508) 293-7786
> > > black_david@emc.com        Mobile: +1 (978) 394-7754
> > > ----------------------------------------------------
> > >
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