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

<Black_David@emc.com> Mon, 01 March 2010 22:53 UTC

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Date: Mon, 1 Mar 2010 17:53:22 -0500
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Thread-Topic: SCSI Version Descriptors - iSCSI and SAM-5
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Subject: [storm] SCSI Version Descriptors - iSCSI and SAM-5
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<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.

David L. Black, Distinguished Engineer
EMC Corporation, 176 South St., Hopkinton, MA  01748
+1 (508) 293-7953             FAX: +1 (508) 293-7786
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