Re: [storm] SPC-2 reserve/release: Proposed text - version 4
"Black, David" <david.black@emc.com> Wed, 26 September 2012 15:47 UTC
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From: "Black, David" <david.black@emc.com>
To: "Knight, Frederick" <Frederick.Knight@netapp.com>, "storm@ietf.org" <storm@ietf.org>
Date: Wed, 26 Sep 2012 11:46:38 -0400
Thread-Topic: SPC-2 reserve/release: Proposed text - version 4
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Subject: Re: [storm] SPC-2 reserve/release: Proposed text - version 4
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That text looks good to me, but I have one more minor change ... ... I'd prefer to put the second paragraph at the end of 4.4.3.1, as it applies to all nexus state not just reservations: The specific Unit Attention condition that results from session re-establishment indicates whether or not nexus state was preserved, see Section 6.3.4 of [SAM4]. Thanks, --David > -----Original Message----- > From: Knight, Frederick [mailto:Frederick.Knight@netapp.com] > Sent: Wednesday, September 26, 2012 11:40 AM > To: Black, David; storm@ietf.org > Subject: RE: SPC-2 reserve/release: Proposed text - version 4 > > Yes, I think we've got it. Since I can't define "an extended period of time", > here's my take: > > - When connection failure causes the iSCSI session to fail, and > the session is not reinstated or continued, target retention > of that session's reserve/release reservation state > may require an initiator to issue a > reset (e.g., LOGICAL UNIT RESET, see section 11.5) in order > to remove that reservation state. > > The specific Unit Attention condition that results from session > re-establishment indicates whether or not nexus state was preserved, > see Section 6.3.4 of [SAM4]. > > Along with: > > OLD > > That is, it should perform session recovery as > > described in Chapter 6. > > NEW > > That is, it should recover the session via connection > > reinstatement as described in Section 6.3.4. > > END > > Fred > > > -----Original Message----- > From: Black, David [mailto:david.black@emc.com] > Sent: Wednesday, September 26, 2012 10:51 AM > To: Knight, Frederick; storm@ietf.org > Subject: RE: SPC-2 reserve/release: Proposed text - version 4 > > Fred, > > > I don't see anywhere that these timers are associated with any SCSI > > state, or with the RESERVE state. Attempting to tie RESERVE state to > > these timers is a NEW requirement. Our goal here was specifically to > > NOT create any new requirements. > > I think you have a point that this is too specific. What if we just delete > mention of those timers? The bullet in question could then simply say: > > - When connection failure causes the iSCSI session to fail, and > the session is not reinstated or continued, target retention > of that session's reserve/release reservation state for an > extended period of time may require the initiator to issue a > reset (e.g., LOGICAL UNIT RESET, see section 11.5) in order > to remove that reservation state. > > That captures the primary concern that I wanted to alert implementers to. > > > We do not want to impact existing iSCSI implementations. Could we > > associate the action that occurred with the observable behavior the > > host sees? I don't like putting SCSI layer stuff in a transport layer > > spec, but it should just be informative. > > The text that follows explicitly lists the SCSI ASC/Q values (e.g., 29/07, in > hex). That's something I'd prefer to avoid, e.g., as T10 could easily add > additional ASC/Q values that are relevant to this situation. > > As an alternative, I suggest that we state the principle and point to SAM-4 > for the details, e.g., add the following text to the end of 4.4.3.1: > > The specific Unit Attention condition that results from session > re-establishment indicates whether or not nexus state was preserved, > see Section 6.3.4 of [SAM4]. > > Would that be ok? > > Thanks, > --David > > > -----Original Message----- > > From: Knight, Frederick [mailto:Frederick.Knight@netapp.com] > > Sent: Wednesday, September 26, 2012 8:39 AM > > To: Mallikarjun Chadalapaka; Black, David; storm@ietf.org > > Subject: RE: SPC-2 reserve/release: Proposed text - version 4 > > > > I'm concerned about this new link between Time2Wait and RESERVE state. > > Such a link has not previously existed. I don't think we should > > create such a linkage. > > > > Section 4.6.3.3 includes: > > .... In addition, the Logout Response indicates how long the target > > will continue to hold resources for recovery (e.g., command execution > > that continues on a new connection).... > > > > This and many other places where Time2Wait and Time2Retain are > > discussed, the points all have to do with command continuation; no > > mention of I_T state, or RESERVE state, or mode pages, or anything else. > > > > Section 7.5 says: > > .... Time2Wait is the initial "respite time" before attempting an > > explicit/implicit Logout for the CID in question or task reassignment > > for the affected tasks (if any).... > > > > Or, task reassignment of affected tasks; with no mention of I_T state. > > > > Section 7.6 ties the termination of tasks to the Time2Wait / > > Time2Retain timers. Section 11.14.5 makes the same statements about > > the task termination linkage to those timers. > > > > Section 11.15.3 says those timers are "...the minimum amount of time, > > in seconds, to wait before attempting task reassignment.". > > > > Section 8.3 defines Session State. And there is one sentence that I > > can find in all 345 pages that associates that session state with > > these timers. It is in section 11.15.4 where it says: If it is the > > last connection of a session, the whole session state is discarded after > Time2Retain. > > > > I don't see anywhere that these timers are associated with any SCSI > > state, or with the RESERVE state. Attempting to tie RESERVE state to > > these timers is a NEW requirement. Our goal here was specifically to > > NOT create any new requirements. > > > > We do not want to impact existing iSCSI implementations. Could we > > associate the action that occurred with the observable behavior the > > host sees? I don't like putting SCSI layer stuff in a transport layer > > spec, but it should just be informative. Something like: > > > > If the initiator receives a UA: 29/00 or 29/01 or 29/04 then the > > RESERVE state has been lost. (Maybe 29/04 belongs in a RESERVE state > unknown list). > > > > If the initiator receives a UA: 29/07 then the RESERVE state has been > > preserved. > > > > I didn't list 29/02 or 29/03 or 29/05 or 29/06 since I view those as > > Parallel SCSI specific. We can debate which items belong in which > > list, but would this kind of observable behavior approach be better > > than a new requirement? FYI - I didn't invent this; I copied it from > > SAM-5r11 (sub-clause 6.3.4) where it states it as a requirement on the > > target - that when an I_T NEXUS LOSS event occurs, if the state is > > retained, 29/07 is returned, and if the state is not retained, then 29/01 is > returned. > > > > We also don't want to create any new requirement now in this > > consolidated draft that conflicts with this SAM-5 text, since we will > > eventually have to comply with SAM-5 and its follow-ons. > > > > Another approach would be to ignore this for the consolidated draft, > > and force it into the iSCSI-SAM draft - which references SAM-4 and > > SAM-5 where I_T Nexus loss is already defined and the above text already > exists. > > > > Fred > > > > -----Original Message----- > > From: storm-bounces@ietf.org [mailto:storm-bounces@ietf.org] On Behalf > > Of Mallikarjun Chadalapaka > > Sent: Tuesday, September 25, 2012 9:39 PM > > To: Black, David; storm@ietf.org > > Subject: Re: [storm] SPC-2 reserve/release: Proposed text - version 4 > > > > Looks good to me overall. Two minor comments: > > > > 1) For 4.4.3.1, I have replaced the current sentence with the > > following one (instead of the proposed): > > > > That is, it should reinstate the session via iSCSI session > > reinstatement (Section 6.3.5) or continue via session continuation (Section > 6.3.6). > > > > 2) For proposed new text, I have tweaked the version 4 sentence below, > > keeping the existing implementations in view: > > > > VERSION 4: > > The Time2Wait and Time2Retain > > timeout values (see Section 7.55) apply to retention of > reserve/release > > reservation state after iSCSI session failure because that state > > is part of the I_T Nexus state. > > > > VERSION 5: > > Instead, implementations are strongly encouraged to apply the > > Time2Wait and Time2Retain timeout values (see Section 7.5) > > to manage retention of reserve/release reservation state after > > iSCSI session failure because that state is part of the I_T nexus > state. > > > > > > Thanks. > > > > Mallikarjun > > > > > > -----Original Message----- > > From: storm-bounces@ietf.org [mailto:storm-bounces@ietf.org] On Behalf > > Of Black, David > > Sent: Tuesday, September 25, 2012 2:39 PM > > To: storm@ietf.org > > Subject: [storm] FW: SPC-2 reserve/release: Proposed text - version 4 > > > > version 4 changes: > > > > More changes for Mallikarjun's comments, mostly a rewrite of the first > > additional caveat bullet. I've chosen not to reference Annex B of > > SPC-4 as that seems a bit far afield for a SCSI transport standard like > iSCSI. > > > > version 3 changes: > > > > Responding to Mallikarjun's comments (plus some more edits) - > > > > > 1) IMHO, opening sentence of "I_T nexus state includes reservation state" > > > is a little too broad, > > > > I removed that sentence, removed I_T Nexus from new section title and > > tweaked the persistent reservation text to talk about state in general > > as opposed to I_T Nexus state in particular. > > > > > 2) Hard reset is not an LU reset - it is either an iSCSI Target Warm > > > Reset, or (more likely) an iSCSI Target Cold Reset. In either case, > > > any of the three resets should clear the reserve/release state. > > > > I removed the word "hard" - as you noted, an LU reset is sufficient to > > remove a reserve/release reservation. > > > > > 3) Should use Time2Retain+Time2Wait, not Default Time2Wait > > > > Brilliant minds think alike - I got to that one in version 2 ;-). > > > > > 4) Session recovery does not necessarily preserve the I_T nexus > > > state (recovery may not occur within Time2Wait+Time2Retain, and may > > > not use the same ISID when it occurs), but session reinstatement and > > > session continuation certainly should. > > > > I changed "session recovery" to "session reinstatement". > > > > > 5) Should articulate the underlying linkage between Time2Retain (an > > > iSCSI concept), and the reserve/release state (a SCSI state). > > > > I believe I also got to that one in version 2. > > > > version 2 changes: > > > > I moved a paragraph break in response to Ralph's comments, and rewrote > > the first additional consideration to reference the connection timeout > > values in general. I also found some minor problems that need > > correction in Section > > 4.6.3.3 (see end of this message). > > > > --- version 4 follows --- > > > > <WG chair hat off> > > > > Here's an initial attempt to propose text to deal with the reserve/ > > release topic in the consolidated iSCSI draft. Please comment, > > correct, suggest edits, etc. > > > > The new text would be a new section 4.4.3.2 that would follow 4.4.3.1: > > > > 4.4.3.1. I_T Nexus State > > > > Certain nexus relationships contain an explicit state (e.g., > > initiator-specific mode pages) that may need to be preserved by > > the device server [SAM2] in a logical unit through changes or > > failures in the iSCSI layer (e.g., session failures). In order for > > that state to be restored, the iSCSI initiator should reestablish > > its session (re-login) to the same Target Portal Group using the > > previous ISID. That is, it should perform session recovery as > > described in Chapter 6. This is because the SCSI initiator port > > identifier and the SCSI target port identifier (or relative target > > port) form the datum that the SCSI logical unit device server uses > > to identify the I_T nexus. > > > > ------------------------------- > > > > First, for clarity, the following change should be made in the above > > 4.4.3.1 text to better identify the recovery mechanism: > > > > OLD > > That is, it should perform session recovery as > > described in Chapter 6. > > NEW > > That is, it should recover the session via connection > > reinstatement as described in Section 6.3.4. > > END > > > > I believe that a lower-case "should" remains appropriate for this text. > > > > ----------------------------------- > > > > NEW TEXT (second draft): > > > > 4.4.3.2. Reservations > > > > There are two reservation management methods defined in the SCSI > > standards, reserve/release reservations, based on the RESERVE and > > RELEASE commands [SPC2], and persistent reservations, based on the > > PERSISTENT RESERVE IN and PERSISTENT RESERVE OUT commands [SPC3]. > > Reserve/release reservations are obsolete [SPC3] and SHOULD NOT be > > used; persistent reservations SHOULD be used instead. > > > > State for persistent reservations is required to persist > > through changes and failures at the iSCSI layer that result in > > I_T Nexus failures, see [SPC3] for details and specific requirements. > > > > In contrast, [SPC2] does not specify detailed persistence > > requirements for reserve/release reservation state after an I_T > > Nexus failure. Nonetheless, when reserve/release reservations are > > supported by an iSCSI target, the preferred implementation approach > > is to preserve reserve/release reservation state as part of the > > I_T Nexus state for iSCSI session reinstatement (see Section 6.3.5) > > or session continuation (see Section 6.3.6). > > > > Two additional caveats apply to reserve/release reservations: > > > > - When connection failure causes the iSCSI session to fail, and > > the session is not reinstated or continued, target retention > > of that session's reserve/release reservation state for an > > extended period of time may require the initiator to issue a > > reset (e.g., LOGICAL UNIT RESET, see section 11.5) in order > > to remove that reservation state. The Time2Wait and Time2Retain > > timeout values (see Section 7.55) apply to retention of > reserve/release > > reservation state after iSCSI session failure because that state > > is part of the I_T Nexus state. The need for resets in this > > scenario may be reduced by suitable selection of values for > > these two timeouts. > > > > - Reserve/release reservations may not behave as expected when > > persistent reservations are also used on the same logical unit; > > see the discussion of "Exceptions to SPC-2 RESERVE and RELEASE > > behavior" in [SPC4]. > > > > ----------------------- > > > > Reference impacts: both [SPC2] and [SPC3] need to be normative > > references, but [SPC4] can be an informative reference. > > > > ------------------------- > > > > I deliberately used "the preferred iSCSI implementation approach" > > wording for reserve/release reservation state preservation > > requirements, as > > SPC-2 is vague on this topic and I'm rather uncomfortable with placing > > a requirement as strong as a "SHOULD" on an obsolete mechanism that "SHOULD > NOT" > > be used. > > > > --------------- > > > > New problem in Section 4.6.3.3 - in this text: > > > > The Logout response indicates that the connection or session > > cleanup is completed and no other responses will arrive on the > > connection (if received on the logging out connection). In > > addition, the Logout Response indicates how long the target will > > continue to hold resources for recovery (e.g., command execution > > that continues on a new connection) in the text key Time2Retain > > and how long the initiator must wait before proceeding with > > recovery in the text key Time2Wait. > > > > Time2Wait and Time2Retain are not text keys - they're binary fields in > > the Logout Response PDU. Two changes are in order: > > - "text key Time2Retain" -> "Time2Retain field" > > - "text key Time2Wait" -> "Time2Wait field" > > > > 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 > > ---------------------------------------------------- > > > > _______________________________________________ > > storm mailing list > > storm@ietf.org > > https://www.ietf.org/mailman/listinfo/storm > > > > _______________________________________________ > > storm mailing list > > storm@ietf.org > > https://www.ietf.org/mailman/listinfo/storm > > > > _______________________________________________ > > storm mailing list > > storm@ietf.org > > https://www.ietf.org/mailman/listinfo/storm > > > > _______________________________________________ > > storm mailing list > > storm@ietf.org > > https://www.ietf.org/mailman/listinfo/storm > > > > > > _______________________________________________ > > storm mailing list > > storm@ietf.org > > https://www.ietf.org/mailman/listinfo/storm >
- [storm] FW: SPC-2 reserve/release: Proposed text … Black, David
- Re: [storm] SPC-2 reserve/release: Proposed text … Mallikarjun Chadalapaka
- Re: [storm] SPC-2 reserve/release: Proposed text … Knight, Frederick
- Re: [storm] SPC-2 reserve/release: Proposed text … Black, David
- Re: [storm] SPC-2 reserve/release: Proposed text … Knight, Frederick
- Re: [storm] SPC-2 reserve/release: Proposed text … Black, David
- Re: [storm] SPC-2 reserve/release: Proposed text … Knight, Frederick
- Re: [storm] SPC-2 reserve/release: Proposed text … Julian Satran
- Re: [storm] SPC-2 reserve/release: Proposed text … Julian Satran
- Re: [storm] SPC-2 reserve/release: Proposed text … Julian Satran