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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: iSCSI: Canonical TargetsMark, I am not sure that we want to have your "canonical" target as a mandatory construct. It is good for proxies, routers, portals etc.? Don't the have better mechanisms for discovery. But why should you force it on some small box that has the name wired and printed on it's label. To reach the canonical you have to go through all the "login etc.". I think that all goes back to asking - why should we use iSCSI for discovery? SLP, UPnP, Salutation, Jini all attempt discovery using a a general form (good for iSCSI, Lpr printers etc.) Can't we take the same path? Julo Mark Bakke <mbakke@cisco.com> on 12-05-2001 00:04:24 Please respond to Mark Bakke <mbakke@cisco.com> To: IPS <ips@ece.cmu.edu> cc: Subject: iSCSI: Canonical Targets It was pointed out during the interim meeting that the canonical target is defined somewhat ambiguously, and may be a bit too flexible for interoperability purposes. This message is a stake in the ground for defining this a little more tightly. So here are the new canonical target rules. Please let me know if there are major problems with any of them. I tried to define them a-la-carte, to make it easier to pick out any that might cause trouble. 1. Each iSCSI implementation MUST include a canonical target. 2. A canonical target MUST be accessible at the default, IANA- assigned TCP port on each IP address on which the iSCSI implementation is listening for iSCSI connections. 3. A canonical target MUST NOT be used for SCSI commands. A canonical target is an iSCSI construct only, and does not have a corresponding SCSI device. This means it may not be used to access Logical Units. A session created to a canonical target is a discovery session only, and once in full feature phase, is used only for text commands and asynchronous messages. (Do any other commands make sense)? 4. A device containing a single target MUST provide both the canonical target and the real target. (This is implied by the above requirements). An initiator connecting to such a device using only its IP address would first connect to the canonical target, and use SendTargets to obtain the iSCSI name of the real target. It would then create a separate session to the real target. Essentially, this means there's nothing special about a single-target device. 5. An iSCSI device MUST provide a unique iSCSI name for each of its targets. Using the canonical target as a nameless iSCSI target is not supported. 6. We can further specify the order in which the SendTargets response fields are returned, to simplify things further, e.g. each target in the SendTargets response MUST return these fields in this order: - A TargetName= field - A TargetAlias= field (value left blank if there's no alias) - One or more TargetAddress= fields - Any vendor-specific fields (ignored by standard initiators) The above rules will make the behavior of various target implementations identical, regardless of the number of interfaces or targets they support. This will reduce the number of end-cases that initiator implementations will have to handle. If we agree on these, we can edit them into the iSCSI and NDT documents. Additional questions to send input on: 1. Should a non-canonical target respond to a SendTargets command? 2. If so, should it respond only with addresses for its own target, or should it respond with other targets, as a canonical target might do? 3. If not, the initiator must connect to a canonical target to find the other addresses of a target to which it is already connected; is the information it has sufficient to do so? (I think the answer is yes, given canonical requirement #2 above). -- Mark A. Bakke Cisco Systems mbakke@cisco.com 763.398.1054
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