[storm] iSCSI version descriptors

<david.black@emc.com> Fri, 22 October 2010 05:14 UTC

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From: <david.black@emc.com>
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Date: Fri, 22 Oct 2010 01:14:39 -0400
Thread-Topic: iSCSI version descriptors
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Subject: [storm] iSCSI version descriptors
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One more time on this issue.  This is for discussion - it's not an announcement of a decision.  This is the only real issue that needs to be resolved to complete the new (SAM) features draft for iSCSI.

Reminder: we need to define a set of small positive integer values to describe the iSCSI version starting with 0 = "no version claimed".  After some private discussions, it appears that we need two additional version values beyond 0.

The first observation is that the baseline should be at least RFC 3720 (original iSCSI) + RFC 5048 (Corrections and Clarifications).  That would be version value 1.

The next observation is that taking features out of the consolidated iSCSI draft may allow a visible behavior change.  RFC 3720 has this to say about text keys for negotiation:

   All keys in this document, except for the X extension formats, MUST
   be supported by iSCSI initiators and targets when used as specified
   here.  If used as specified, these keys MUST NOT be answered with
   NotUnderstood.

When we take out a feature in the new iSCSI consolidated draft, the easiest thing to do is allow a NotUnderstood response to the keys that negotiate that feature.  This should not pose a problem for unimplemented features, but it would be a behavior change.  The completely backwards-compatible alternative is have the consolidated iSCSI draft list the keys used for removed features and prohibit  a NotUnderstood response to those keys (Reject would be an acceptable alternative response).

If we're careful about this, the same version value can apply to 3720/5048 and the consolidated iSCSI draft.  I'd suggest that we be careful, and the details of how can be worked out as we finalize the consolidated draft - I think we should have at least one more round of looking at features to remove.

After that, we'll need a version value for the new (SAM) features draft additions.  The result would be 3 version values:
	0 = no version claimed
	1 = 3720/5048 or new consolidated draft
	2 = (3720/5048 or new consolidated draft) + SAM 4/5 features from the SAM draft.

Comments?

The SAM 4/5 features draft will expire while draft submission is closed for the Beijing meeting - if we can resolve this issue, the next version of that draft could be submitted shortly after draft submission opens again, and would probably go to WG Last Call shortly thereafter.

Thanks,
--David
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David L. Black, Distinguished Engineer
EMC Corporation, 176 South St., Hopkinton, MA  01748
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