SORT BY:

LIST ORDER
THREAD
AUTHOR
SUBJECT


SEARCH

IPS HOME


    [Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

    iSCSI: abort task & abort task set


    • To: "ips" <ips@ece.cmu.edu>
    • Subject: iSCSI: abort task & abort task set
    • From: "Mallikarjun C." <cbm@rose.hp.com>
    • Date: Sun, 2 Dec 2001 15:33:18 -0800
    • Content-Transfer-Encoding: 7bit
    • Content-Type: text/plain;charset="iso-8859-1"
    • Sender: owner-ips@ece.cmu.edu

    Julian,
    
    iSCSI currently requires two responses to be returned for an aborted task -
    one for the original task with a "good" status, and the second for the task
    management function (TMF) itself.  So, the following legal behaviors are
    required of a target -
        a) plug the CmdSN gap if the command was not received,
        b) send a SCSI response and TMF response if the task still is active,
        c) send a TMF response if the task isn't active (if already complete).
    
    I would like to suggest that we reconsider our approach for case (b) for
     a variety of reasons, to change it to:
        b) send a TMF response signalling that the abort is complete, if the
    task
            still is active.
    
    Here are my reasons -
    
        1. Target iSCSI layer would need to make a SCSI response up on
            an abort of an active task.  It then follows that the iSCSI layer
            may have to make up several SCSI responses on an 'abort task set'.
    
       2.  The current approach also creates a side effect that isn't readily
            apparent for 'abort task set'.  Initiators would need to stall
    processing
            'abort task set' TMF response till task responses (to account for
    all
            the tasks in the task set) on multiple TCP connections (possibly on
            different NICs) are received - which I am afraid would tantamount to
            an initiator scoreboard.
    
        3. The current approach complicates initiator implementations that want
            to process a successful SCSI completion even after they initiated
            timeout processing since on an 'abort task set', initiators can
    never
            be sure if the response was pre-abort, or post-abort (made up "good"
            status).  I believe it is worth preserving this implementation
    choice.
    
       4.  I am further concerned that iSCSI is possibly in violation of the
    spirit of
            SAM-2, rev20.
             - clause 5.6.2 that states -
    "When an initiator causes its own task(s) to be aborted, no notification
    that the task(s) have been aborted shall be
    returned to the initiator other than the completion response for the command
    or task management function action
    that caused the task(s) to be aborted and notification(s) associated with
    related effects of the action (e.g., a target
    reset unit attention condition)."
    
             - clause 5.3.1 that states -
    "GOOD. This status indicates that the device server has successfully
    completed the task."
    
    I propose that the target deliver only the TMF response on an abort of
    an active task on an 'abort task' TMF, and not transmit an 'abort task set'
    TMF response until all the current StatSN's on all connections (as on the
    completion of "abort task set') in the session are ack'ed.  This ack may be
    solicited by way of a NOP-IN with valid TTT.
    
    This gives the determinism to initiators that  (a) abort task set TMF
    response
    signifies that the entire task set had been dealt with, and (b) every task
    response
    is a true SCSI end-to-end reponse (not generated by iSCSI), besides doing
    away with SCSI-response code in the target iSCSI layer.
    
    Comments?  Did I miss any corner cases?
    
    Regards.
    --
    Mallikarjun
    
    Mallikarjun Chadalapaka
    Networked Storage Architecture
    Network Storage Solutions Organization
    Hewlett-Packard MS 5668
    Roseville CA 95747
    
    


Home

Last updated: Mon Dec 03 08:17:43 2001
7979 messages in chronological order