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    StatSN and overlapped commands


    • To: ips@ece.cmu.edu
    • Subject: StatSN and overlapped commands
    • From: dcuddihy@attotech.com
    • Date: Tue, 5 Aug 2003 09:45:43 -0400
    • Content-type: text/plain; charset=us-ascii
    • Delivered-To: ips-outgoing@sos.ece.cmu.edu
    • Delivered-To: ips-outgoing@ece.cmu.edu
    • Delivered-To: ips@sos.ece.cmu.edu
    • Delivered-To: ips@ece.cmu.edu
    • Sender: owner-ips@ece.cmu.edu

    I have a question about the lifespan of SCSI tasks on ISCSI.  My apologies
    if it's been addressed on the reflector previously.
    
    Put simply, is a SCSI task considered completed when status is returned to
    the initiator, or when status is acknowledged via ExpStatSN?
    
    This causes a difference in behavior for untagged SCSI commands.  Consider:
    
    Initiator: SCSI Command = Write: Attr = Untagged (0) : InitiatorTaskTag=5:
    CmdSN=4: ExpStatSn = 3
    Target:  R2T: InitiatorTaskTag = 5
    Initiator: SCSI Data: Initiator Task Tag = 5
    Target: SCSI Status = Good:  Initiator Task Tag = 5: StatSn = 3
    Initiator: Scsi Command = Write: Attr = Untagged (0) : Initiator Task Tag
    = 6: CmdSN=5: ExpStatSn = 3
    .
    .
    (Somewhere down the line a scsi command with ExpStatSN of 4 is sent, ACKing
    the Status to ITT #5)
    .
    .
    
    Is this an overlapped command error, since the SCSI task is still
    oustanding until the status is acknowledge?
    Or -- is the SCSI command considered completed as soon as status is
    attempted (much like the clearing of a Congingent Allegiance as soon as
    status is started to the host)?  That would mean that this is a legal
    exchange.  If so, does this cause problems with command recovery as
    described in section 3.2.2.2 ?
    
    Thanks!
    
    david
    
    
    
    David J Cuddihy
    Principal Engineer
    ATTO Technology, Inc.
    http://www.attotech.com/fcbridge.html
    dcuddihy@attotech.com
    
    
    
    


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Last updated: Tue Aug 05 12:54:07 2003
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