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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] RE: FW: iSCSI: "conservative reuse" requirementDue to 2.5.3 (b) "Between a given SCSI initiator port and SCSI target port, there can be only one I_T nexus (session)", aren't we always "assuming no more than one session"? Or are you talking about more than one session between different SCSI initiator ports and a single SCSI target port? Is the ISID equivalent to SAM-2's Initiator Port Identifier? Eddy -----Original Message----- From: Jim Hafner [mailto:hafner@almaden.ibm.com] Sent: Friday, December 28, 2001 12:15 PM To: John Hufferd; Eddy Quicksall; Mallikarjun C.; Black_David@emc.com Cc: ips@ece.cmu.edu Subject: Re: FW: iSCSI: "conservative reuse" requirement Folks, Sorry for taking so long to jump into this discussion. There are a number of issues raised in this thread: 1) should "conservative reuse" of ISIDs be made a MUST 2) does "conservative reuse" imply that all hosts look "single SCSI ported" Here's my two cents (using "CR" as a shorthand for "conservative reuse") I don't believe that CR needs to be a MUST. The only time this has any real value is in configurations that use SCSI persistent reservations (and where new SCSI target reservation features are enabled -- NB. these features are yet to be approved but are working their way through the process). I don't think these are going to be (even in the future) the majority of installations. There are many ways then that CR could be something that is not generally available in most drivers but is added by configuration and perhaps even "value add" (:-{)). In short, I don't see a strong case for this to be a MUST. So, to David Black, my answer is that having a mechanism to enable this feature or have it as a "purchase requirement" is an acceptable mechanism to make sure the feature is there when needed, but it is need not be a requirement of the protocol. To Mallikarjun, I think I'm agreeing with you that so long as there is a mechanism defined, iSCSI has done it's job. As for the second issue (raised by Mallikarjun), let's look at the definition of CR. What is means is that when an iSCSI initiator (node) creates ISIDs for use in session identifiers, it attempts to reuse them as much as possible with different SCSI target ports (iSCSI target portal groups). This is the only way that a SCSI target or LU can see the same SCSI initiator port through two or more of its SCSI target ports -- that is, that the target can determine multiple paths *from* the same SCSI initiator port. But, the model for generating ISIDs is not really at the node level but at the initiator portal group level. So, IMO, the conclusion that all hosts must then look "single SCSI ported" is too dramatic. As I mentioned, ISIDs are conceptually generated within initiator portal groups (that's why we defined the mechanism for generating ISIDs). The conclusion I draw is that (assuming no more than one session to any given target portal group), an iSCSI initiator implementing CR will have as many SCSI initiator ports as iSCSI initiator portal groups (independent HBAs?). Each initiator portal group would generate one ISID (that is different from that generated by/for the other initiator portal groups) and use CR for repeatability. [This is consistent with a model that mapped SCSI initiator ports to initiator portal groups, which we had to abandon because the "assuming no more than one session..." was no acceptable as a requirement!!!] This independence of ISIDs for each initiator portal group allows each initiator portal group to open sessions with *every* target portal group it knows about without having to worry about interfering with other sessions. [This has shades of the "partitioning" rule for ISIDs that has been discussed ad nauseum!!!] (I have a feeling that this note is not well composed -- it is the holidays, you know). I hope I've addressed everyone's concerns and we can lay this one to rest. Jim Hafner John Hufferd 12/25/2001 08:49 AM To: "Eddy Quicksall" <Eddy_Quicksall@iVivity.com> cc: Jim Hafner/Almaden/IBM@IBMUS From: John Hufferd/San Jose/IBM@IBMUS Subject: Re: FW: iSCSI: "conservative reuse" requirement (Document link: Jim Hafner) You are correct. The section was created by Jim Hafner, and via this note I will ask him if he could answer Mallikarjun Directly since I did not understand his issue. . . . John L. Hufferd Senior Technical Staff Member (STSM) IBM/SSG San Jose Ca Main Office (408) 256-0403, Tie: 276-0403, eFax: (408) 904-4688 Home Office (408) 997-6136, Cell: (408) 499-9702 Internet address: hufferd@us.ibm.com "Eddy Quicksall" <Eddy_Quicksall@iVivity.com> on 12/24/2001 06:06:44 PM To: John Hufferd/San Jose/IBM@IBMUS cc: Subject: FW: iSCSI: "conservative reuse" requirement John, Were you the author of "conservative reuse"? I am wondering about some issues. Maybe you could educate me somewhat ... I started this subject in a different thread by saying that it may be good to make "conservative reuse" a MUST. I got one objection from Santosh below. Then David Black picked it up by basically agreeing with me. Then Mallikarjun objected to that. It seems like the objective would be to give targets a way to figure out that two or more sessions are coming from the same Initiator Port. That is needed support persistent reservations. If an initiator does not use "conservative reuse", I don't think targets will be able to make that determination. Comments? Eddy -----Original Message----- From: Mallikarjun C. [mailto:cbm@rose.hp.com] Sent: Monday, December 24, 2001 12:47 AM To: Black_David@emc.com Cc: ips@ece.cmu.edu Subject: Re: iSCSI: "conservative reuse" requirement > I think this is headed towards "conservative reuse" being a MUST if > we're serious about support for shared persistent reservations. Mandating "conservative reuse" appears to force initiators to always act as a single initiator port (wrt one target; assuming only one session as an example) per initiator device - which rules out the case of an initiator intentionally wanting to present a different port to each target portal group. IMHO, if iSCSI provides an architected mechanism to support shared persistent reservations ("conservative reuse"), that should be completely adequate to meet the expectations to be a legal SCSI protocol. -- Mallikarjun Mallikarjun Chadalapaka Networked Storage Architecture Network Storage Solutions Organization Hewlett-Packard MS 5668 Roseville CA 95747 ----- Original Message ----- From: <Black_David@emc.com> To: <santoshr@cup.hp.com> Cc: <ips@ece.cmu.edu> Sent: Friday, December 21, 2001 4:50 PM Subject: iSCSI: "conservative reuse" requirement > Santosh Rao writes: > > > I am opposed to the suggestion that "conservative re-use" of ISIDs be > > made a MUST. This is really only required when initiators need to be > > using the new T10 Reservation scheme that can be shared > > across initiator ports. > > Those reservations are a Target feature. With this approach, the ability > to use the target feature depends on details of the initiator > implementation. > More below ... > > > For those initiators that don't care about this type of reservation, > > conservative re-use is of no use and initiators may like to assign > > ISID's in a per-initiator node fashion, thereby, being able to use these > > ISIDs as a lookup index for the sessions on that initiator node. > > > > Hence, I suggest that "conservative re-use" be worded as > > "encouraged to use" or something to that effect, but not MUST USE. > > > > Comments ? > > The "initiator" is more than one entity. The iSCSI HBA/NIC and driver > doesn't know whether shared persistent reservations are being used and > shouldn't have to care - they're just more SCSI commands to transport. > Some other entity (e.g., clustering software) will be generating the > shared persistent reservations. This raise the possible scenario > involving a target that supports the new shared persistent reservations > and an entity that wants to use them. The entity detects (via SCSI means, > e.g., something in a mode page) that the Target supports shared persistent > reservations, tries to use them, only to discover that they don't work > because the iSCSI HBA/NIC doesn't implement "conservative reuse". > > I'm worried about this causing both interoperability issues and possible > T10 issues -- from a T10 viewpoint, if shared persistent reservations > don't work, the initiating entity should have some SCSI-level means > of determining this ... if that means exists only on the Target, the > above scenario is iSCSI's problem (Target can't query Initiator to > determine whether it does "conservative reuse"), and having a separate > initiator side means that the entity has to check only for iSCSI (and > not for any other SCSI transport) does not seem like the right > approach. > > I think this is headed towards "conservative reuse" being a MUST if > we're serious about support for shared persistent reservations. > > Comments? > --David > --------------------------------------------------- > David L. Black, Senior Technologist > EMC Corporation, 42 South St., Hopkinton, MA 01748 > +1 (508) 249-6449 *NEW* FAX: +1 (508) 497-8500 > black_david@emc.com Cell: +1 (978) 394-7754 > --------------------------------------------------- > >
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