Re: [storm] iSCSI version descriptors

Mallikarjun Chadalapaka <cbm@chadalapaka.com> Mon, 07 March 2011 22:12 UTC

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From: Mallikarjun Chadalapaka <cbm@chadalapaka.com>
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Date: Mon, 7 Mar 2011 14:13:28 -0800
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Subject: Re: [storm] iSCSI version descriptors
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David,

In trying to determine what if any text needs to change in the consolidated
spec after this discussion, I did a re-reading of this whole thread - up to
DavidH's most recent note.   I stumbled on the following:

>  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).

I do not believe the consolidated spec needs to change the current
negotiation semantics.  I suggest a third option: 
1) When a feature is completely obsoleted (e.g. markers) relative to 3720,
iSCSI consolidated spec requires that the corresponding keys be negotiated
to "No" (e.g. OFMarker=No).

2) When a feature *option* is obsoleted (e.g. SPKM1 & SPKM2 for AuthMethod),
the spec does nothing special.    The existing iSCSI negotiation semantics
are comprehensive enough that two spec-compliant implementations will
negotiate to the correct result because the obsoleted options for that
feature are not offered as negotiables.


This should minimize the core protocol changes, and related impacts to
existing interop tests.
 
Comments are welcome.  With the fast-approaching Prague deadline, I will go
ahead with the spec'ing this option if I don't hear any disagreement on this
by this Wednesday.

Thanks.

Mallikarjun




  -----Original Message-----
  From: storm-bounces@ietf.org [mailto:storm-bounces@ietf.org] On Behalf
  Of david.black@emc.com
  Sent: Thursday, October 21, 2010 10:15 PM
  To: storm@ietf.org
  Subject: [storm] iSCSI version descriptors
  
  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
  ----------------------------------------------------
  David L. Black, Distinguished Engineer
  EMC Corporation, 176 South St., Hopkinton, MA  01748
  +1 (508) 293-7953             FAX: +1 (508) 293-7786
  david.black@emc.com        Mobile: +1 (978) 394-7754
  ----------------------------------------------------
  
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