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    RE: iSCSI: Use of the A bit



    
    
    yes - I think that the latest text does just that. Julo
    
    
                                                                                                             
                          "Rod Harrison"                                                                     
                          <rod.harrison@win        To:       Julian Satran/Haifa/IBM@IBMIL, John Hufferd/San 
                          driver.com>               Jose/IBM@IBMUS                                           
                                                   cc:       "Mallikarjun C." <cbm@rose.hp.com>,             
                          18-03-02 23:29            <ips@ece.cmu.edu>, <owner-ips@ece.cmu.edu>               
                          Please respond to        Subject:  RE: iSCSI: Use of the A bit                     
                          "Rod Harrison"                                                                     
                                                                                                             
                                                                                                             
    
    
    
    
                 Can we explicitly allow the status and data ACKs to be at the
    same
    time? Otherwise we prevent sending the status ACK (expStatSn) in the
    data ACK SNACK PDU.
    
                 - Rod
    
    -----Original Message-----
    From: owner-ips@ece.cmu.edu [mailto:owner-ips@ece.cmu.edu]On Behalf Of
    Julian Satran
    Sent: Monday, March 18, 2002 8:23 PM
    To: John Hufferd
    Cc: Mallikarjun C.; ips@ece.cmu.edu; owner-ips@ece.cmu.edu
    Subject: Re: iSCSI: Use of the A bit
    
    
    
    John,
    
    comments in text - JUlo
    
    
    John Hufferd/San Jose/IBM@IBMUS
    18-03-02 19:17
    Please respond to John Hufferd
    
            To:        Julian Satran/Haifa/IBM@IBMIL
            cc:        "Mallikarjun C." <cbm@rose.hp.com>,
    ips@ece.cmu.edu, owner-ips@ece.cmu.edu
            Subject:        Re: iSCSI: Use of the A bit
    
    
    
    
    
    Julian the following statement is confusing:
    
    "An initiator MUST ONLY acknowledge the status for command that
    produced
    Data-In PDUs after acknowledging the Data-In PDUs if Data-In PDU
    acknowledgment is requested by the target.  A status acknowledgement
    for a
    command that generated Data-In PDUs is considered by the target as an
    implicit acknowledgement of the Data-In PDUs if such an
    acknowledgement
    was requested by the target."
    
    What did you intend to say.  All commands MUST have t status
    acknowledge,
    via ExpStatSN, so I do not understand the first sentence.  And if the
    Data-In PDUs must be acknowledged (if the A bit is set), what is the
    meaning of the last statement.
    
    +++ The first statement says that IF data-ack is requested it MUST be
    sent by the initiator before it acknowledges status.
    +++
    
    Since I do not believe there is a need to ack the last Data-In PDU, I
    am
    hoping you agree.  But it is not clear.
    
    
    +++
    In fact the target may want a data ack as the status ack might be
    delayed for various reasons.
    The second statement says that if the target sees a status ack that is
    also an ack for the data
    
    The first statement says that the initiator must send ack if asked -
    and send status ack only afterwards.
    
    The second says that when status is received the data are acked and
    target should wait no longer (i.e., no recovery action).
    +++
    If the Target sets the A bit on the last Data-In PDU, which also has
    good
    status set -- and the Initiator has a PDU ready to send to which it
    can
    attach the value of ExpStatSN, which will show that the Data-In PDU
    was
    received -- there should be no reason to send a extra SNACK for the
    Data-In
    PDU.
    
    Please tell me that is what you intended to say in the above quoted
    text.
    
    
    .
    .
    .
    John L. Hufferd
    Senior Technical Staff Member (STSM)
    IBM/SSG San Jose Ca
    Main Office (408) 256-0403, Tie: 276-0403,  eFax: (408) 904-4688
    Home Office (408) 997-6136, Cell: (408) 499-9702
    Internet address: hufferd@us.ibm.com
    
    
    "Julian Satran" <Julian_Satran@il.ibm.com>@ece.cmu.edu on 03/17/2002
    05:52:46 PM
    
    Sent by:    owner-ips@ece.cmu.edu
    
    
    To:    "Mallikarjun C." <cbm@rose.hp.com>
    cc:    ips@ece.cmu.edu, owner-ips@ece.cmu.edu
    Subject:    Re: iSCSI: Use of the A bit
    
    
    
    Dear all,
    
    The text for the A bit part (9.7.2) reads now:
    
      A (Acknowledge) bit
    
    
          For sessions with ErrorRecoveryLevel 1 or higher, the target
    sets
          this bit to 1 to indicate that it requests a positive
          acknowledgement from the initiator for the data received.  The
          target should use the A bit moderately; it MAY set the A bit to
    1
          only once every MaxBurstSize bytes or on the last Data-In PDU
    that
          concludes the entire requested read data transfer for the task
    from
          the target's perspective, and MUST NOT do so more frequently
    than
          this.
    
          On receiving a Data-In PDU with the A bit set to 1, the
    initiator
          MUST issue a SNACK of type DataACK.  If the initiator has
    detected
          holes in the input sequence, it MUST postpone issuing the SNACK
    of
          type DataACK until the holes are filled. An initiator MUST ONLY
          acknowledge the status for command that produced Data-In PDUs
    after
          acknowledging the Data-In PDUs if Data-In PDU acknowledgment is
          requested by the target. A status acknowledgement for a command
    that
          generated Data-In PDUs is considered by the target as an
    implicit
          acknowledgement of the Data-In PDUs if such an acknowledgement
    was
          requested by the target.
    
    The ITT mandating text in 9,16.1 will read:
    
          For Status SNACK and DataACK, the Initiator Task Tag is
    reserved. In
           all other cases, the Initiator Task Tag field MUST be set to
    the
          Ini-tiator Task Tag of the referenced command.
    
    
          Julo
    
    
    
    
    
    
    
    


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Last updated: Mon Mar 18 18:18:12 2002
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