Re: [storm] SCSI Version Descriptors - iSCSI and SAM-5

"Mallikarjun Chadalapaka" <> Mon, 08 March 2010 07:05 UTC

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From: "Mallikarjun Chadalapaka" <>
To: "'Knight, Frederick'" <>, <>, <>
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Date: Sun, 7 Mar 2010 23:05:49 -0800
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Subject: Re: [storm] SCSI Version Descriptors - iSCSI and SAM-5
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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.



> -----Original Message-----
> From: [] On Behalf Of
> Knight, Frederick
> Sent: Tuesday, March 02, 2010 10:20 AM
> To:;
> Subject: Re: [storm] SCSI Version Descriptors - iSCSI and SAM-5
> I agree, we need to request a frozen SAM-5 version descriptor, and see
> they say.
> I'm reluctant to create a new descriptor to indicate compliance with
> old (3720+5048).
> All those existing implementations that support 3720+5048 will NOT have
> descriptor.  What is an initiator to think?  How will the initiator tell
> old compliant device that supports 3720+5048 with no descriptor from the
> 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
> then the device must NOT be 3720+5048 compliant.
> I'm reluctant to punish existing compliant devices by creating a
> that they will not report.  The horse is already out of the barn, what
> 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 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: []
> Sent: Monday, March 01, 2010 5:53 PM
> To:
> Subject: [storm] SCSI Version Descriptors - iSCSI and SAM-5
> <WG Chair Hat On>
> We have some interesting technical decisions to make around asking for
> 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
> 4).  A version descriptor value specifies both a standard and a revision.
> Version descriptor values are defined by explicit action at T10; this
> as an indirect control over which versions of standards to which a device
> claim to comply, and discourages compliance with revisions that are
> or otherwise unsuitable.  T10 only assigns version descriptors to drafts
> standards that T10 believes to be stable (e.g., suitable to implement
> The straightforward decision is that the iSCSI features update 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.
> 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
> and bring the resulting recommendation to the storm WG list and the
> 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
> known to be inbound.
> The more interesting decision is version descriptors for iSCSI.
> there's only a generic version descriptor value , 0x960h "iSCSI (no
> claimed)".  There are an additional 31 descriptor values available to
> and so the question to the storm WG is - what would we like to see
> I have two initial suggestions:
> 1) I suggest asking that a version descriptor be defined for the
> 	of RFC 3720 (iSCSI) and RFC 5048 (iSCSI corrections and
> 	to enable a device to claim that it has implemented RFC 5048.  We
> 	add additional RFCs to this set, e.g., RFC 3980 for NAA names,
> 	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
> 	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
>        Mobile: +1 (978) 394-7754
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