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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: iSCSI: proposal to solve the ISID issuesI have no problem with the Must have a way to have the Node name set. However, I do not grasp the problem you state here: "I don't believe the type of the ISID matters, nor does the NIC capability (coordinating vs not). If two initiator NICs share the same node name, they better not re-use the same ISID to a given target portal group. I was trying to capture the consequences of this reality." If the ISID includes the Vendor ID, I do not see the problem, unless the vendor can not assign the rest of the ISID. And I would say that it is the vendors problem to work out. If you are saying that with NICs (not HBAs) that the SW Drivers will have a problem coming up with the ISID, I do not understand that either since most software is built by a Vendor, and if not the Random type should work. Now in case you are saying something about the creation of a second Session from the Initiator, which is to access the same Target Node. Then by definition, the ISID must be unique. (and it will probably need a Wedge Driver to operate correctly). I would think that a vendor should be able to come up with a unique qualifier for the session since they have 64K numbers to chose from. Remember the vendor only needs to coordinate the lower 2 bytes of the new ISID, with itself. So if they can not do that, ... Oh well ... Are we on the same page yet? . . . 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 Internet address: hufferd@us.ibm.com "Mallikarjun C." <cbm@rose.hp.com>@core.rose.hp.com on 10/29/2001 06:35:55 PM Please respond to cbm@rose.hp.com Sent by: cbm@core.rose.hp.com To: John Hufferd/San Jose/IBM@IBMUS cc: ips@ece.cmu.edu Subject: Re: iSCSI: proposal to solve the ISID issues John, I take it that you don't have an issue with the Node Name part of the wording. I thought I answered your question by saying - "My point though is that by banning a duplicate nexus (that an inadvertently re-used ISID allows), we are making the ISID (dynamic/static) distribution an imminent hard requirement for all NICs in a given iSCSI initiator Node" The unspoken assumption above is that we would want to allow multiple sessions between an initiator node and a target portal group. I don't believe the type of the ISID matters, nor does the NIC capability (coordinating vs not). If two initiator NICs share the same node name, they better not re-use the same ISID to a given target portal group. I was trying to capture the consequences of this reality. Regards. -- Mallikarjun Mallikarjun Chadalapaka Networked Storage Architecture Network Storage Solutions Organization MS 5668 Hewlett-Packard, Roseville. cbm@rose.hp.com John Hufferd wrote: > > Mallikarjun, > I do not understand the purpose for your proposed wordage > > "All iSCSIinitiator hardware implementations MUST in addition also support > the operational ISID values to be (either statically or dynamically) > externally configurable." > > Why is this so important that it is a MUST. The purpose of the proposal is > to eliminate the need for the above. At most it should only apply to the > vendors (Probably Software and at Universities and IT shops) that use the > RANDOM ISID type code. > > I do not see the need elsewhere. At most it could be "MAY". > > . > . > . > 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 > Internet address: hufferd@us.ibm.com > > "Mallikarjun C." <cbm@rose.hp.com>@ece.cmu.edu on 10/29/2001 05:24:20 PM > > Please respond to cbm@rose.hp.com > > Sent by: owner-ips@ece.cmu.edu > > To: Jim Hafner/Almaden/IBM@IBMUS > cc: ips@ece.cmu.edu > Subject: Re: iSCSI: proposal to solve the ISID issues > > Jim, > > Thanks for the quick response. > > As much as I would like to avoid consuming more bandwidth > on this topic, let me make one last strawman for wording below. > > > What words do you suggest? > ... > > And a lot depends on how > > functional the NICs are: (a) just network nics, (b) protocol nics, but > not > > session coordinating nics (c) full session coordination nics (with driver > > assist) (d) fully autonomous session nics. How do we make a requirement > > that fits all the cases correctly? > > I have been implying iSCSI NICs in all my postings so far - > sorry, may be that wasn't very clear. "iSCSI Node name" comment > obviously wasn't targeted at simple network NICs. So clearly (a) > is out of discussion. But you are right - I wasn't very precise. > Here's a strawman - > > All iSCSI hardware implementations (as in NICs) MUST allow > the iSCSI Node Name to be externally configurable. All iSCSI > initiator hardware implementations MUST in addition also > support the the operational ISID values to be (either statically > or dynamically) externally configurable. > > > Making them configurable (at > > initialization time, e.g., as a range of values) or making them dynamic > > (the driver generates them on demand) both fit the mold. So, I don't > think > > this one is a hard requirement. > > I agree that my earlier "range" wording was too constraining. > My point though is that by banning a duplicate nexus (that an > inadvertently re-used ISID allows), we are making the ISID > (dynamic/static) distribution an imminent hard requirement > for all NICs in a given iSCSI initiator Node - except it is > not sufficiently explicit. Please consider the above proposed > wording. > > > Well, I don't think so. If each vendor implements "conservative reuse" > > within their own ISID namespace on their own NICs, then you get this > > property system wide. > > You are right, I guess I briefly overlooked the fact that ISID > includes the vendor identifier within, per the new proposal. > > I am personally okay with making "conservative reuse" a > SHOULD. > > Regards. > -- > Mallikarjun > > Mallikarjun Chadalapaka > Networked Storage Architecture > Network Storage Solutions Organization > MS 5668 Hewlett-Packard, Roseville. > cbm@rose.hp.com > > Jim Hafner wrote: > > > > Mallikarjun, > > > > Comments in line below > > > > Jim Hafner > > > > "Mallikarjun C." <cbm@rose.hp.com>@core.rose.hp.com on 10/29/2001 > 12:17:49 > > pm > > > > Please respond to cbm@rose.hp.com > > > > Sent by: cbm@core.rose.hp.com > > > > To: Jim Hafner/Almaden/IBM@IBMUS > > cc: ips@ece.cmu.edu > > Subject: Re: iSCSI: proposal to solve the ISID issues > > > > Jim, > > > > Thanks for the excellent summary. Some questions/comments - > > > > - I assume that the NICs must enable the configuration of > > iSCSI Node name even in this proposal. If it is so, please > > call this out as a hard requirement in the main modelling > > discussion. > > > > <JLH> > > This requirement doesn't change from before (but how it gets written into > > the spec may differ -- and we've had this discussion before). If a > vendor > > doesn't allow configuration of his NIC's iSCSI Node name, then his NICs > > will be acting as their own iSCSI Node (that is, not representing the > > system they live in). One can argue that this is a legitimate > > implementation (just as writing user-level code that uses its own iSCSI > > Node name). So a "hard requirement" may be a bit too strong. However, I > > will go with the will of the group on this point. > > > > What words do you suggest? > > </JLH> > > - In the case of multiple NICs from the same vendor operating > > in an end node, it appears to me that the proposal implicitly > > assumes an ISID-range to be configurable among those NICs > > (perhaps in vendor-unique ways, which is always what I expected). > > If this is a correct inference, there is again a hard > > requirement on the NICs to make the ISID range configurable. > > Please comment on any subtle qualitative change from the > > earlier situation that I may be missing. > > > > <JLH> > > Well, the point is that the vendor can manage his own namespace for his > > NICs anyway he/she/it wants to. Making them configurable (at > > initialization time, e.g., as a range of values) or making them dynamic > > (the driver generates them on demand) both fit the mold. So, I don't > think > > this one is a hard requirement (though that is probably how most vendors > > will implement their NICs). In effect, the proposal gives vendors more > > flexibility in their own space, without causing heterogenous > > interoperability problems within the host. And a lot depends on how > > functional the NICs are: (a) just network nics, (b) protocol nics, but > not > > session coordinating nics (c) full session coordination nics (with driver > > assist) (d) fully autonomous session nics. How do we make a requirement > > that fits all the cases correctly? You clearly have in mind a specific > > level of implementation within the NICs, but that may not be everybody's > > model. > > </JLH> > > > > > (2-e) Its debatable whether "conservative reuse" is a MUST or a > > > SHOULD. My personal opinion is "SHOULD", because many systems, > > > particularly low-end that don't use reservations, can function more or > > > less OK without it. > > > > It seems we're attempting to set ourselves up for future in > > discussing the above requirement. Some questions - > > - It appears to me that the "conservative reuse" can not > > be enforced for initiators hosting NICs from different > > vendors (since the proposal allows ISID namespaces to > > be totally non-overlapping between non-homogenous NICs). > > Is this a fair assessment? > > <JLH> > > Well, I don't think so. If each vendor implements "conservative reuse" > > within their own ISID namespace on their own NICs, then you get this > > property system wide. As before, by owning their own piece of the ISID > > namespace, they can implement what they want. So, you may have a > situation > > where some of your installed nics have this property and some don't. > > You'll find out (if your environment really needs conservative reuse) > that > > you haven't got it, and it becomes a marketing/purchase spec requirement. > > </JLH> > > - Do you see a particular disadvantage for low-end systems > > if it's mandated (aside from the fact that they may be able > > to live without it)? > > <JLH> > > No, but I don't see any way to really enforce it (or even really test > it). > > It's not a requirement of the protocol, per se. > > </JLH> > > - Do you see any corner cases not being met (for future) > > if we don't make it a MUST (since you said "more or less OK")? > > <JLH> > > No, I can't see that far into the future! :-{). One reason I'm being > cagey > > here is that I'm finding it difficult to find the right words to specify > > this as a hard requirement (but I'm no technical writer either!). > > </JLH> > > > > Regards. > > -- > > Mallikarjun > > > > Mallikarjun Chadalapaka > > Networked Storage Architecture > > Network Storage Solutions Organization > > MS 5668 Hewlett-Packard, Roseville. > > cbm@rose.hp.com > > > > Jim Hafner wrote: > > > > > > Folks, (David Black in particular). > > > > > > Apologies for the long note, but the issue is complicated. > > > > > > The NDTeam have a proposal to resolve the concerns surrounding use of > > > ISIDs as essential components (along with iSCSI Initiator Name) of > > > SCSI Initiator Portname. (This was rooted in private discussions > > > between John Hufferd, Julian and myself -- and came about as a result > > > of the lengthy (and boring) discussions mostly myself and David > > > Black.) > > > > > > There are two somewhat orthogonal issues involved in this discussion: > > > > > > 1) How to coordinate ISIDs in the initiator to minimize the risk of > > > accidentally breaking the ISID RULE (no parallel nexus) when > > > independent vendors co-exist in the same OS. > > > > > > 2) What ISID "reuse" rules should be specified to facilitate current > > > and future (soon?) SCSI reservation semantics (and also internal OS > > > views of SCSI Initiator Ports). > > > > > > To address these two issues, we (NDT) propose the following: > > > > > > 1) Enlarge the ISID field in the Login Request and Response to 6bytes > > > and structure it with a component that corresponds to a "naming > > > authority" (essentially the vendor generating the ISID). So vendors > > > each have a piece of the ISID namespace to work with their own > > > components (HBAs, SW, etc). More details below. > > > > > > 2) ISIDs (within the namespace of a given iSCSIName) SHOULD be used as > > > conservatively as possible ("conservative reuse"). What this means is > > > that a given ISID should be reused for as many sessions (across > > > multiple target portal groups) as possible (but never to the same > > > target portal group twice -- that's the ISID RULE). > > > > > > NOTES and ADVANTAGES: > > > > > > (1-a) Each vendor owns his own piece of the ISID namespace, so in > > > effect, at the vendor-level, this provides a "partitioning" of that > > > namespace. > > > > > > (1-b) We don't need to specify an OS infrastructure requirement for > > > configuration of ISIDs -- each vendor can do it any way it chooses > > > (within its naming authority). > > > > > > (1-c) Breaking of the ISID RULE will only occur if a vendor messes up > > > its own implementation. > > > > > > (1-d) This is not fundamentally different from David Black's > > > suggestion for a "key"; it just (a) defines it precisely and (b) > > > embeds it in an already defined (but enlarged) field. > > > > > > (1-e) Looking towards the future, as common ISID coordination > > > mechanisms are implemented between vendors (say, SNIA banding together > > > to define a precise API), this "naming authority" can be elevated to > > > the coordinating entity or even the OS vendor. > > > > > > (1-f) ISIDs have no global uniqueness property. They need only be > > > unique between a named iSCSI initiator and iSCSI target portal group. > > > That means that a vendor implementation can use the same algorithm to > > > generate ISIDs (under its naming authority) in every machine (OS). > > > > > > (2-a) If a SCSI target (or logical unit) is holding state (say > > > persistent reservation) for a SCSI Initiator Port (named by iSCSI Name > > > and ISID), and the associated nexus/session is dropped for some > > > reason, "reuse" by that initiator of that ISID will restore to the > > > resulting new session that state (with no other action on the part of > > > the upper SCSI layers). > > > > > > (2-b) "Reuse" of an ISID on different sessions to (necessarily) > > > different SCSI Target Ports (iSCSI Target portal groups), will enable > > > the SCSI target/logical unit to recognize a common SCSI Initiator Port > > > for those two paths. This facilitates future changes to SCSI > > > reservations (at least). > > > > > > (2-c) An initiator driver implementated with "conservative reuse" can > > > present to the OS a stable and fairly static view of the SCSI > > > Initiator Ports (one for each ISID). Current OS driver stacks > > > (including current wedge drivers) that are built on the presumption of > > > such a stable view, will not need modification to handle the more > > > dynamic nature of iSCSI's SCSI Initiator Port. [Note: the existence of > > > a SCSI Initiator Port presented to the OS does not *require* that this > > > port discover all possible targets; what the initiator builds sessions > > > to using a specific ISID will determine what is presented to the OS as > > > "devices" and LUs visible to that SCSI Initiator Port (could be none > > > if that ISID is never actually used!).] > > > > > > (2-d) (Related to (2-c)): Adding a new (pseudo-static) SCSI Initiator > > > Port is as simple as configuring another ISID! > > > > > > (2-e) Its debatable whether "conservative reuse" is a MUST or a > > > SHOULD. My personal opinion is "SHOULD", because many systems, > > > particularly low-end that don't use reservations, can function more or > > > less OK without it. This is an open question. > > > > > > DETAILS: > > > > > > 1) ISID Structure: > > > The 6byte ISID structure would be split into three parts: > > > "type" field (1byte) -- identifies the format of the naming > > > authority field > > > "naming authority" field (3bytes) -- identifies the vendor (or > > > group of vendors) generating this ISID > > > "qualifier" (2bytes) -- the free-space for ISID uniqueness > > > > > > The type field takes on three defined values with all other values > > > reserved: > > > Type naming authority format > > > 00h IEEE OUI > > > 01h IANA Enterprise Number (EN) > > > 02h "Random" > > > > > > The first types two provide a mechanism to uniquely (world wide) > > > identify the naming authority. A vendor with one or more OUIs and > > > possibly also Enterprise number MUST use at least one of these numbers > > > when it generates ISIDs. > > > > > > The "Random" type is for the case where the ISID generator (SW or HW) > > > is provided by an entity that has no OUI or EN. This includes, for > > > example, > > > -- a user-written program that builds sessions (and has access to the > > > system level iSCSI Name) > > > -- a university or other organization providing the component > > > -- a testing tool > > > > > > For the "Random" type, the naming authority field should be a random > > > or pseudo-random number. (See below on how this affects "conservative > > > reuse"). > > > > > > [Note: the "type" field needn't be this big, but NDT felt that (a) > > > 2bits was insufficient for the future, (b) the "type" field should be > > > first, and (c) the "naming authority" field should be byte-aligned.] > > > > > > 2) Conservative Reuse > > > > > > The "conservative reuse" principle of this proposal just says that > > > SCSI Initiator Portnames should be viewed as static things (as much as > > > possible) and reused (when feasible) to give the most stable > > > presentation of SCSI Initiator Ports to both the OS above and to SCSU > > > targets across the wire. > > > > > > Whereas the current draft says "The ISID RULE does not preclude the > > > use of the same ISID to different Target portal groups", the > > > "conservative reuse" requirement would say that such reuse (using the > > > same ISID to many target portal groups) is a SHOULD (or is that > > > MUST?). So, in one implementation, each iSCSI Initiator Portal group > > > would get configured with iSCSI Name, and a (small) set of ISIDs. The > > > portal group might take this set of ISIDs as an ordered list. The > > > first session to a Target portal group would use the first ISID, the > > > second to the *same* target portal group would use the second in the > > > list, etc. The number of ISIDs would then define a configuration > > > parameter that can be interpreted as the maximum number of sessions > > > that can be built to a given target portal group. > > > > > > To facilitate "conservative reuse", the "qualifier" field of a set of > > > ISIDs SHOULD be generated using either a repeatable algorithm > > > (non-random or pseudo-random but based on a fixed seed) or any > > > algorithm and stored in a persistent location (e.g., registry or /etc > > > file). > > > > > > For the "Random" type, "conservative reuse" may not be an issue (say, > > > user application that doesn't care about reservations, etc.). When it > > > is, the "naming authority" field SHOULD also be generated by a > > > mechanism similar to that for the "qualifier" field as specified above > > > (e.g., defined in the SW at compilation time.) > > > > > > DOCUMENTATING CHANGES: > > > > > > The iscsi drafts would need the following minor changes to support > > > this proposal: > > > > > > NDT doc > > > (a) define the structure of the ISID field (as described above) > > > (b) add some notes about implementation in the presense of > > > "conservative reuse" (e.g., that ISID should be configured once, say > > > at install time, then reused on subsequent reboots, even for "Random" > > > type). > > > > > > iSCSI MAIN doc: > > > (a) move the CID field in Login Request to another reserved field. > > > (b) expand the ISID field in Login Request and Response to encompass > > > the previous 4 bytes. > > > (c) add a sentence where the ISID field is defined indicating that > > > this field is a structured value, showing the structure (as above) and > > > point to the NDT document. > > > (d) add some text to "Note to Implementors" on "conservative reuse". > > > > > > Comments? > > > > > > Jim Hafner -- Mallikarjun Mallikarjun Chadalapaka Networked Storage Architecture Network Storage Solutions Organization MS 5668 Hewlett-Packard, Roseville. cbm@rose.hp.com
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