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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: iSCSI : login keys & mode page settingsSantosh, Comments in text. Julo Santosh Rao <santoshr@cup.hp.com> on 18/04/2001 02:19:27 Please respond to Santosh Rao <santoshr@cup.hp.com> To: IPS Reflector <ips@ece.cmu.edu> cc: T10 Reflector <t10@t10.org> Subject: iSCSI : login keys & mode page settings All/Julian, The iSCSI draft is lacking sufficient description on the subject of mode page settings specific to iSCSI, their corresponding iSCSI login keys and the interactions between these 2 mechanisms. Specific comments enclosed below in that regard : 1) The iSCSI draft needs to describe the layout of the protocol specific mode pages, namely, disconnect-reconnect mode page, protocol specific lun page and protocol specific port page as applicable to iSCSI. Such a figurative and textual description should be along the lines of that in FCP-2 Section 10. +++ I don't know what version you are reading - both 5.91and 92 have them. +++ 2) Specifically, the iSCSI draft lacks the description of the layout of the protocol specific lun page and in its absence, then describes a field from this page called EnableCmdRn. This field is non-existent in the SPC-2 description of this page in Section 8.3.10. +++ See above - this is a protocol specific page +++ 3) On a side note, the EnableCmdRN & CmdRN fields should be re-named to EnableCRN and CRN to reflect the same semantics and context as the CRN defined in SAM-2 and FCP-2. +++ what's in a name... +++ 4) The EnableCmdRN login key should be removed from the list of iSCSI login keys as this is a per-LUN key and iSCSI login keys have the scope of a session. IOW, EnableCmdRN should be negotiated through a mode select only and not through iSCSI login. +++ I realized this and you are reading old stuff !!+++ 5) On a more fundamental note, should iSCSI allow for 2 levels of control of I-T[-L] nexus operational parameters thru both the mode select/sense scsi mechanisms and iSCSI login key mechanisms ? +++ It is all about function - several people felt that the (primitive) negotiation element in the text commands is better than trying to set a parameter to an unacceptable value and finding this out through a mode sense ++++ Ex : --------------------------------------------------------------------- iSCSI login key SCSI mode page parameter --------------------------------------------------------------------- DataPDULength - Max Burst Size (Disc-reconn mode page) FirstBurstSize - First Burst Size (disc-reconn mode page) InDataOrder - EMDP (disconn-reconn mode page) EnableCmdRN - Enable CRN (LUN control mode page) If such control is to be allowed at both the SCSI ULP and iSCSI transport layers, a communication mechanism should be defined to synchronize the state of these operational parameters across the 2 layers when a change is made in either layer through its corresponding mechanisms. Ex : a) Change thru iSCSI login key should result in an up call to update the SCSI ULP. b) Change made thru mode select should result in a down call to update iSCSI LLP. c) Change thru iSCSI login key should result in an up call to SCSI ULP to cause a UNIT ATTENTION indicating "Mode Parameters Changed". +++ I view the ULP as the source for generating the text comands through a new interface (give some credit to implementers). Whenever this is not the case the SCSI will use the old mode set commands. ISCSI will not set parameters by its own +++ 6) If such a level of dual control is provided, the iSCSI login keys listed above be made LO (leading only) to allow for changes to operational parameters only during session login. This is to minimize/eliminate disruption of ongoing I/O activity that occurs due to the generation of a UNIT ATTENTION CHECK CONDITION when any change is made to the above paramters. 7) If only 1 mechanism of control is desired, which of the following alternatives is desirable : i) Only settable thru mode select and seen thru mode sense Pros : ------ - Allows 1 mechanism of control. - Removes the need for synchronization of these values across SCSI ULP & iSCSI. Cons : ------ - Requires setting for all LUNs to enable for the entire session. ii) Settable thru iSCSI and also settable/viewable thru mode sense. Pros : ------ - flexible and allows control thru both scsi & iSCSI. Cons : ------ - Can lead to synchronization overheads. - Needs SP(save page) setting also to be communicated in synching iSCSI login to mode page values. iii) Only settable thru iSCSI and viewable thru mode sense. Pros: ----- - Single mechanism of modification avoiding synchronization issues in setting. Cons : ------ - Denies traditional mechanism of modification. (mode sense). - May break existing applns if enforced thru SPC-2. - Requires changes to SPC-2. - iSCSI compliance requires changes in SCSI ULP for SPC-2 compliance of the change to not use mode select for parameter changes that are shared with iSCSI. 8) If these operational parameters are allowed to be set thru iSCSI login and they also impact mode page settings, iSCSI spec should describe the scope of the mode page setting in terms of whether this setting is a saved page setting or not ? 9) Should saved page settings be allowed thru iSCSI ? - Santosh - santoshr.vcf
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