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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] iSCSI: Immediate Delivery BehaviorHi: The behavior for immediate commands seems ambiguous and possibly needlessly complex. Rev 06 says the following regarding ordered delivery to the SCSI layer: "Except for the commands marked for immediate delivery the iSCSI target layer MUST deliver the commands to the SCSI target layer in the order specified by CmdSN. Commands marked for immediate delivery may be handed over by the iSCSI target layer to the SCSI target layer as soon as detected. iSCSI may avoid delivering some command to the SCSI layer if so required by some prior SCSI or iSCSI action (e.g., clear task set Task Management request received before all the commands it was supposed to act on)." In a non-striped session consisting of one TCP/IP connection, the above could be interpreted to allow the delivery of an immediate command before other partly received commands that were previously issued. As a result, an operation, such as an abort task, might bypass the command to be aborted -- even if both were sent on the same connection. Assuming that's true, I believe a useful simplification is to require that all traffic flowing over a given TCP/IP connection be delivered to the SCSI layer in the order received over that connection. In a striped session, an immediate command might therefore leapfrog commands on other connections but would never bypass commands on the same connection. In my opinion, that simplifies the problem of properly purging commands and stale PDUs in the wake of a task management operation. Charles Charles Monia Senior Technology Consultant Nishan Systems email: cmonia@nishansystems.com voice: (408) 519-3986 fax: (408) 435-8385
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