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    Re: iSCSI : On the subject of R2T and Task Tags.



    
    
    Answers in text  - Julo
    
    Santosh Rao <santoshr@cup.hp.com> on 08/01/2001 05:34:52
    
    Please respond to Santosh Rao <santoshr@cup.hp.com>
    
    To:   IPS Reflector <ips@ece.cmu.edu>
    cc:
    Subject:  iSCSI : On the subject of R2T and Task Tags.
    
    
    
    
    On the subject of R2T and task tags .....
    
    Section 2.16. R2T
    =============
    1) Differing nomenclatures "Target Task Tag" and
    "Target Transfer Tag" for the same field. Only 1 of the 2 should
    be used. The current semanticsof this field seem to call for a
    "Target R2T Tag" name and not a "Target Task Tag",
    since this is not per task.
    
    <js> will fix </js>
    
    2) The READ I/O PDUs do not use a "Target Task Tag".
    The WRITE I/O PDUs use a "Target Task Tag" per R2T
    and not per task.
    
    It seems like the only unique per I/O identifier is the Initiator
    Task Tag. (?) Is it the intention of iSCSI that targets should be
    using the Initiator Task Tag as the per I/O lookup tag ?
    
    If this is true, then, the name "Initiator Task Tag" is a misnomer
    and it should just be "Task Tag", since it is used by both initiators
    and
    targets.
    <js> We use initiator and target for the task to state who is "generating"
    the tag </js>
    Explicitly stating the semantics of "Target Task Tag" in
    Section 2.2 would help, particularly since, it seems like iSCSI's
    concept of "Target Task Tag" differs from the semantics of the
    equivalent(?) RX_ID in the Fibre Channel header.
    
    iSCSI seems to be more closely aligned with Parallel SCSI's
    single Queue Tag model than Fibre Channel's OX_ID/RX_ID
    tag model.
    <js> iSCSI is completely neutral to the targets use of the target transfer
    tag
    it can follow both models. The iSCSI protocol treats the as an opaque
    handle to
    give back to the target to do the association.
    </js>
    3) Quoting from the draft :
    "The present document does not limit the number of outstanding
    datatransfers."
    
    As we had discussed earlier, this needs to be removed, since
    MaxOutstandingR2T bounds the number of outstanding R2Ts.
    <js> will remove the offending statement </js>
    Thanks,
    Santosh
    
     - santoshr.vcf
    
    
    
    


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