|
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: iSCSI: Question on StatRN usageMallikarjun, Thanks for your comments. Initiator scoreboarding is not considered. I will try to emphasize this even more in the new draft. The party responsible for reporting length is the target. As overlapping ranges are not explicitly forbidden this would be a harder task than apparent. Reporting counts becomes entirely a question of faith! Regards, Julo "Mallikarjun C." <cbm@rose.hp.com> on 20/10/2000 05:40:16 Please respond to cbm@rose.hp.com To: ips@ece.cmu.edu cc: Subject: Re: iSCSI: Question on StatRN usage Julian, Thanks for the clarifications, I am pleased to understand that there's no overloading of any reference #s - the usage of new term "DataRN" in your new draft makes it a lot clearer. Some comments. >Mallikarjun and Prasanjit, > >Sorry for the confusion. > >The text is confusing and I have corrected it the new text. StatRN is >mandatory (it is the only way we have to ACK status and is not related to >ordering). Eventhough StatRN itself may not be used by an initiator for ordering (unless it wants to order completions, for whatever reason), StatRNs are themseleves are in a monotonically increasing order. It is helpful to state this explicitly. > >As for the data the intent was to use StatRN to just number data packets >for a given command (start with whatever you want) and have them acked with >a NOP with the same task tag (this is important for input data for which we >have no other way of acking them). Those numbers are not related to the >Status numbers. No ordering or recovery is required up to command restart. >I assume that numbers will not wrap unless a target sends more blocks than >bytes (and it can!) but even then >no harm is done. >At recovery the restarted command will be followed by a NOP with the same >initiator tag indicating what is the >the block expected. The initiator does not have to do any scoreboardong >only keep the counters. >The target can free early resources and iSCSI can recover eve long reads. >For writes evidently R2T does the job but it means that write data can be >recovered only with R2T. This implies that in case an iSCSI implementation is counting the # of bytes transferred in/out during a task, it shall not assume an error if the count is the less than expected transfer size - if the retry bit was set (This is especially true for writes, where the initiator doesn't know from which point target starts issuing R2Ts). I would suggest adding this comment as well to enable better interoperability. >Should we overload on CmdRN/ExpCmdRN to shorten recovery? I don't see a >need. NO, I don't see either. My concern was that overloading these RNs for data would become a scalability bottleneck, when a session spans mulitple NICs. I am glad that it's not what was intended. Comments on your next email: >The NOP message PDUs are not associated with a task, are meant for >immediate delivery, and their only purpose is synchronizing the ordering >registers of the target and initiator. I would like to point out that NOP PDUs are indeed associated with a task! They are associated with a task whose read data they are ack'ing (given that the DataRN is only task-unique). Also, I would like to point out that the current definition of NOP payload does not have Initiator Task Tag - it needs to be added. Thanks. -- Mallikarjun M/S 5601 Networked Storage Architecture HP Storage Organization Hewlett-Packard, Roseville. cbm@rose.hp.com phone: (916) 785-5621 fax: (916) 785-2875
Home Last updated: Tue Sep 04 01:06:36 2001 6315 messages in chronological order |