Re: [storm] Plan for iSCSI work

"Hemal Shah" <hemal@broadcom.com> Thu, 30 June 2011 18:10 UTC

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From: "Hemal Shah" <hemal@broadcom.com>
To: "Mallikarjun Chadalapaka" <cbm@chadalapaka.com>, "Pat Thaler" <pthaler@broadcom.com>, "david.black@emc.com" <david.black@emc.com>, "storm@ietf.org" <storm@ietf.org>
Date: Thu, 30 Jun 2011 11:08:43 -0700
Thread-Topic: [storm] Plan for iSCSI work
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Subject: Re: [storm] Plan for iSCSI work
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Thanks Mallikarjun!

Hemal

-----Original Message-----
From: Mallikarjun Chadalapaka [mailto:cbm@chadalapaka.com]
Sent: Thursday, June 30, 2011 11:06 AM
To: Pat Thaler; Hemal Shah; david.black@emc.com; storm@ietf.org
Subject: RE: [storm] Plan for iSCSI work

Hi Pat,

Thanks for flagging the inconsistency in 10.7, that's a good catch.  Given
that and your/Hemal's feedback, I think turning the current MUST into a
SHOULD is probably the right resolution.   That syncs them both to SHOULD.
Unless I see other comments, I will get this into the next revision.

Thanks.

Mallikarjun


  -----Original Message-----
  From: Pat Thaler [mailto:pthaler@broadcom.com]
  Sent: Wednesday, June 29, 2011 4:03 PM
  To: Mallikarjun Chadalapaka; Hemal Shah; david.black@emc.com;
  storm@ietf.org
  Subject: RE: [storm] Plan for iSCSI work

  Hi Malikarjun,

  10.7 in the consolidated draft says that FastAbort is a SHOULD:
"Therefore,
  both iSCSI target and initiator implementations SHOULD support FastAbort
  multi-task abort semantics (Section 4.2.3.4)."

  When 4.2.3.5 saying "If an iSCSI target implementation is capable of
  supporting TaskReporting=FastAbort functionality" implies that the
  implementation was allowed to not implement FastAbort. You might
  interpret "supporting" = (implemented and negotiated to TaskAbort) as you
  say below, but "capable of supporting" still reads as implemented. When
  the standard puts an if in front of that, it implies that an
implementation is
  allowed to be not capable of supporting FastAbort.

  Neither of these is consistent with MUST implement for FastAbort. The
  rationale for requiring FastAbort doesn't seem strong and I'd prefer that
the
  inconsistency be resolved by not requiring its implementation.

  Regards,
  Pat

  -----Original Message-----
  From: storm-bounces@ietf.org [mailto:storm-bounces@ietf.org] On Behalf
  Of Mallikarjun Chadalapaka
  Sent: Wednesday, June 29, 2011 3:16 PM
  To: Hemal Shah; david.black@emc.com; storm@ietf.org
  Subject: Re: [storm] Plan for iSCSI work

  Hi Hemal,

  >1.     The implementation of TaskReporting is required and NotUnderstood
  response for TaskReporting key is not permitted

  No.  Note that TaskReporting is not defined in RFC 3720.  Patrick
MacArthur
  proposed on this list a couple of weeks ago that we should fix this
  disconnect in the consolidated draft - which I agreed with because I think
  it's a good suggestion.

   >2.    To enable FastAbort on a session, the negotiation of TaskReporting
  key is required.

  Correct, specifically "TaskReporting=FastAbort" must be negotiated.

  >3.     Only when the TaskReporting=FastAbort functionality is supported,
  the protocol behavior specified in Section 4.2.3.4 is required to be
  implemented and exhibited.

  If I were to attempt re-writing your idea, I would say:

  When the protocol behavior specified in Section 4.2.3.4 is implemented and
  TaskReporting=FastAbort is operational on a session, then the FastAbort
  functionality is supported/exhibited on that session by the
implementation.

  >a.     Section 4.2.3.5: If an iSCSI target implementation is capable of
  supporting
  >TaskReporting=FastAbort functionality (Section 13.23).

  "Supporting" = implemented and negotiated to "TaskReporting=FastAbort".
  Note that if even if an implementation has implemented this functionality
  and wants to use it, it will not be able to negotiate it on any session if
it's
  only communicating with a bunch of RFC 3720 implementations.

   >b.    Section 4.2.2.3.3: Whenever the TaskReporting key (Section 12.23
  "Task Reporting") is negotiated to ResponseFence or FastAbort for an iSCSI
  session.
  >c.     Section 4.2.2.3.4: Whenever the TaskReporting key (Section 13.23)
is
  negotiated to ResponseFence or FastAbort for an iSCSI session.

  I don't see an issue.  Note that the discussion in these two sections is
on
  response fencing, not fast abort per se.

  >4.     ...prefixed with some text like "Only when the
  TaskReporting=FastAbort functionality is supported..".

  Please see the above responses.  Your wording is vague for me, as I don't
  comprehend a standalone notion of "supporting" a feature, other than
  implementing a feature and negotiating the feature usage.   Current RFC
  5048
  requirement is that implementation is MUST, and negotiation is MUST
  (may result in the feature to be used, or not).  So as such, there is
already
  ample flexibility for implementations.

  I think you are restating your earlier suggestion to loosen the "MUST
  implement" requirement in RFC5048.  And I've already shared how I feel
  about it, :)  I think it would be a step in the wrong direction, when
faster
  error recovery with multi-task aborts with large # of
sessions/LUs/initiators
  is even more critical, due to increased consolidation in data centers.

  At this point, I think it would be good to also hear from the rest of the
list.

  Thanks.

  Mallikarjun





  >Thanks Mallikarjun! I would still like to confirm my understanding of
  >what
  you describe as "MUST implement, but MUST negotiate".
  >
  >Here is my understanding:
  >
  >1.     The implementation of TaskReporting is required and NotUnderstood
  response for TaskReporting key is not permitted based on the following
text
  from RFC5048 and Section 6.2 of the consolidated draft:
  >                 All keys defined in [RFC3720] MUST be supported by all
  >            compliant implementations; a NotUnderstood answer on any of
  the
  >            [RFC3720] keys therefore MUST be considered a protocol
  > error
  and
  >            handled accordingly.
  >2.     To enable FastAbort on a session, the negotiation of TaskReporting
  key is required.
  >3.     Only when the TaskReporting=FastAbort functionality is supported,
  the protocol behavior specified in Section 4.2.3.4 is required to be
  implemented and exhibited. There are several places in the spec that
  indicate this type of conditionality.
  >a.     Section 4.2.3.5: If an iSCSI target implementation is capable of
  supporting
  >TaskReporting=FastAbort functionality (Section 13.23).
  >b.     Section 4.2.2.3.3: Whenever the TaskReporting key (Section 12.23
  "Task Reporting") is negotiated to ResponseFence or FastAbort for an iSCSI
  session.
  >c.     Section 4.2.2.3.4: Whenever the TaskReporting key (Section 13.23)
is
  negotiated to ResponseFence or FastAbort for an iSCSI session.
  >4.     If TaskReporting=FastAbort functionality is not supported, then
the
  protocol behavior specified in Section 4.2.3.4 is not required to be
  implemented or exhibited. If this is true, then the first sentence in
section
  4.2.3.4 is misleading and should be removed or prefixed with some text
like
  "Only when the TaskReporting=FastAbort functionality is supported..".
  >
  >Hemal
  >
  >
  >-----Original Message-----
  >From: Mallikarjun Chadalapaka [mailto:cbm@chadalapaka.com]
  >Sent: Friday, June 17, 2011 3:32 PM
  >To: Hemal Shah; david.black@emc.com; storm@ietf.org
  >Subject: RE: [storm] Plan for iSCSI work
  >
  >Hi Hemal,
  >
  >During RFC 5048 effort, I recall we settled on the "MUST implement, but
  MUST
  >negotiate" formulation after some list deliberation.
  >
  >With plain RFC 3720 semantics, there are some multi-initiator scenarios
  >where multi-task aborts could essentially lead to target deadlocks,
  >waiting on initiators on third-party sessions that may never respond.
  >With the "Clarified" semantics in RFC 5048, the third-party deadlocks
  >aren't a problem anymore, but issuing initiator could still experience
  >timeouts and escalate error recovery - depending on the number of LUs,
  sessions,
  >connections and tasks affected with the issued TMF.    Escalated error
  >recovery is usually something we want to avoid as it adds more
  >delays/alerts/logs/failovers/failbacks etc.  Finally, "Updated"
  >semantics
  in
  >RFC 5048 are meant to address this timeout problem - they permit
  >targets to provide accelerated responses and allow them to deal with
  >book-keeping/quiescing operations in a lazy fashion (which are the real
  >culprits that trigger timeouts).
  >
  >Given all the above, the WG settled on FastAbort as a MUST-implement.
  >The "MUST negotiate" part then is to enable backwards-compatibility
  >with RFC
  >3720 implementations.  At this point, I'd rather not loosen the
  Consolidated
  >iSCSI draft requirement from what it is in RFC 5048.  I suggest we
  >leave it the way it is.
  >
  >Mallikarjun
  >
  >
  >
  >
  >
  >
  >From: Hemal Shah [mailto:hemal@broadcom.com]
  >Sent: Thursday, June 09, 2011 3:57 PM
  >To: Mallikarjun Chadalapaka; david.black@emc.com; storm@ietf.org
  >Subject: RE: [storm] Plan for iSCSI work
  >
  >Thanks Mallikarjun!
  >
  >The way I read Section 4.1.3 of RFC5048 and Section 4.2.3.4 of the
  >consolidated draft, the implementation of "FastAbort" feature is a MUST.
  >From the first paragraph text from Section 4.1.3 of RFC5048, the first
  >sentence mandates that all iSCSI implementation comply to this section
  >but the second sentence say that the requirement in this section is
  >conditional to the negotiation of "FastAbort" key.
  >
  >Protocol behavior defined in this section MUST be implemented by all
  >iSCSI implementations complying with this document. Protocol behavior
  >defined in this section MUST be exhibited by iSCSI implementations on
  >an iSCSI session when they negotiate the TaskReporting (Section 9.1)
  >key to "FastAbort" on that session.
  >
  >
  >This is confusing. I think it will be better to remove the first
  >sentence from 4.2.3.4 and clarify that the requirements in this section
  >is conditional. I suggest rewording the first two sentences to below:
  >
  >       iSCSI implementations may negotiate the TaskReporting (Section
  >9.1) key to "FastAbort" on an iSCSI session. Protocol behavior defined
  >in this section MUST be exhibited by iSCSI implementations on an iSCSI
  >session when they negotiate the TaskReporting (Section 9.1) key to
  >"FastAbort" on that session.
  >
  >Hemal
  >
  >
  >-----Original Message-----
  >From: Mallikarjun Chadalapaka [mailto:cbm@chadalapaka.com]
  >Sent: Friday, May 27, 2011 5:29 PM
  >To: Hemal Shah; david.black@emc.com; storm@ietf.org
  >Subject: RE: [storm] Plan for iSCSI work
  >
  >Hi Hemal,
  >
  >The text in this draft came verbatim from section 4.1.3 of RFC 5048.
  >There have been no changes in this area.
  >
  >The new text (as well as the old text) requires the TaskReporting key
  >to be negotiated to "FastAbort" before the multi-task abort semantics
  >can be used on an iSCSI session.
  >
  >Thanks.
  >
  >Mallikarjun
  >
  >
  >
  >
  >  -----Original Message-----
  >  From: Hemal Shah [mailto:hemal@broadcom.com]
  >  Sent: Friday, May 27, 2011 4:51 PM
  >  To: Mallikarjun Chadalapaka; david.black@emc.com; storm@ietf.org
  >  Subject: RE: [storm] Plan for iSCSI work
  >
  >  Mallikarjun and David,
  >
  >  I noticed one problematic item in the consolidated draft. This item
  > is
  the
  >  requirement to support FastAbort. This feature was already defined in
  > the  implementation guide, but it was optional. In this draft, it
  > became a  required feature MUST - see in section 4.2.3.4.
  >
  >  Do you know why the requirement was changed in the consolidated
  draft?
  >
  >  I would like to keep the requirement optional as stated in the
  > implementation guide and not break backward compatibility.
  >
  >  Hemal
  >
  >  -----Original Message-----
  >  From: storm-bounces@ietf.org [mailto:storm-bounces@ietf.org] On
  > Behalf  Of Mallikarjun Chadalapaka
  >  Sent: Thursday, May 26, 2011 6:50 PM
  >  To: david.black@emc.com; storm@ietf.org
  >  Subject: Re: [storm] Plan for iSCSI work
  >
  >  Hi David,
  >
  >  The list of changes you have called out are already done in the
  >latest draft.  I
  >  assume then that you are suggesting that the list itself should be
  >included
  >  in the next revision of the draft.
  >
  >  Here's what I recall we have done so far:
  >  1)  iSCSIProtocolLevel specified as "1", and added a related
  >normative
  >  reference to iSCSI-SAM draft
  >  2)  Markers and related keys were removed
  >  3)  SPKM authentication and related keys were removed
  >  4)  Added a new section on responding to obsoleted keys
  >  5)  Have explicitly allowed initiator+target implementations
  >throughout the
  >  text
  >  6)  Clarified that implementations SHOULD NOT rely on SLP-based
  >discovery
  >  7)  Added UML diagrams, and related conventions
  >
  >  The above is of course in addition to consolidating the different
  >RFCs, and
  >  making the related editorial changes.
  >
  >  Thanks.
  >
  >  Mallikarjun
  >
  >
  >
  >
  >    -----Original Message-----
  >    From: storm-bounces@ietf.org [mailto:storm-bounces@ietf.org] On
  Behalf
  >    Of david.black@emc.com
  >    Sent: Friday, May 20, 2011 2:49 PM
  >    To: storm@ietf.org
  >    Subject: [storm] Plan for iSCSI work
  >
  >    I thought I'd offer some advance planning/warning on this, as the
  >    consolidated iSCSI draft (draft-ietf-storm-iscsi-cons) is large
  >(over
  >300
  >    pages).  The current plan is to run a simultaneous WG Last Call on
  >both
  >  this
  >    draft and the new features draft (draft-ietf-storm-iscsi-sam)
  >starting in
  >  mid-
  >    June (probably the week of June 13, after I get back from a badly
  needed
  >    vacation).  That WG Last Call will run longer than the typical
  >2-week time
  >    period, due to the total size of the drafts, but will end by July
  >5th
  at
  >the
  >    latest so that the status of the drafts and the next steps are
  >known prior
  >  to
  >    the T10 (SCSI standards) meetings during the week of July 11.  As
  >July 11th
  >    is also the draft cutoff deadline for the Quebec City IETF
  >meetings, revised
  >    draft versions may not show up until that meeting week (week of July
  >    24th).
  >
  >    This is also a good point to announce that the storm WG will meet in
  >    Quebec City.
  >    I've only requested a 1-hour session, as we get most of our work
  > done
  on
  >    the mailing list.  Among the items for that meeting will be
  > figuring
  out
  >  what
  >    to do with the RDMA extensions draft (despite its name,
  >draft-ietf-storm-
  >    rdmap-ext-00, it's not currently an official work item for the
  >storm WG).
  >
  >    One thing that's missing from the consolidated iSCSI draft (and is
  >a reason
  >    why we're going to need a -03 version) is the changes that it makes
  >to the
  >    RFCs that it consolidates.  Off the top of my head, the major
  >changes
  >are:
  >         - Removal of SPKM authentication
  >         - Removal of the Marker appendix
  >         - Removal of the SHOULD requirement for SLP implementation.
  >    Have I missed anything significant?  The summary of this will need
  >to
  be
  >    added to that draft.
  >
  >    WG Last Call will be an opportunity (in fact the final opportunity)
  > to  discuss
  >    whether anything else should be removed from iSCSI, but there's no
  need
  >    to wait
  >    - I encourage people to review both drafts and post comments
  whenever
  >    they can.
  >
  >    In parallel, work will get started on any iSCSI MIB changes that
  >are needed.
  >    So far, I only see one MIB change - the iSCSIProtocolLevel from the
new
  >    features draft needs to be added to the MIB, probably with a
structure
  >    analogous to the iSCSI version support that's already in the MIB.
  >
  >    Thanks,
  >    --David (storm WG co-chair)
  >    ----------------------------------------------------
  >    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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