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    RE: iSCSI: Use of the A bit



    Nobody in this thread has proposed a "send and ack" design.
    
    Eddy
    
    -----Original Message-----
    From: John Hufferd [mailto:hufferd@us.ibm.com]
    Sent: Saturday, March 16, 2002 3:58 AM
    To: Martins Krikis
    Cc: ips@ece.cmu.edu
    Subject: RE: iSCSI: Use of the A bit
    
    
    
    To any specific user, performance is judged by their own performance not
    the performance of the link or the storage controller over all.
    
    When you read an at-distance disk, and its performance sucks, because of a
    Send and Ack design, you will not have good things to say about iSCSI.  And
    it is not easy to tell what the problem is.  And it is not really possible
    for a customer to determine before purchase that he is buying a poorly
    designed target HBA or chip.  In fact they may have tested it out in a
    local environment and found it OK, and then when contacted by a remote
    initiator, that remote unit is very disappointed.  This gives everyone a
    bad name.  Even if the Links are well used and the overall efficiency of
    the storage controller good, if the individual performance is bad, iSCSI
    will be seen to be bad.
    
    Send and Ack designs are bad designs, and in almost all cases are not
    needed.  And it gives iSCSI a bad name in the environment we have been
    claiming as our own, the at-distance environment.
    
    .
    .
    .
    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
    
    
    Martins Krikis <mkrikis@yahoo.com>@ece.cmu.edu on 03/15/2002 01:45:14 PM
    
    Sent by:    owner-ips@ece.cmu.edu
    
    
    To:    ips@ece.cmu.edu
    cc:
    Subject:    RE: iSCSI: Use of the A bit
    
    
    
    Just a quick note. Some people have implied that the
    use of A-bit necessarily means poor performance.
    
    I would like to disagree. If the target is just
    sitting there waiting for acknowledgment to come
    back before sending the next Data-In sequence, then
    yes, that's poor performance. But I can imagine
    targets that keep sending data while waiting for
    the outstanding acknowledgments. Yes, it requires
    more buffer space, but the acknowledgments are
    actually helpful in managing that bigger buffer space.
    It's a very similar situation to multiple outstanding
    R2T-s. Hopefully everybody agrees that there may be
    benefits to those.
    
    Or am I just missing something again?
    
      Martins Krikis, Intel Corp.
    
    Disclaimer: These opinions are mine and may not
                reflect those of my employer.
    
    
    
    
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Last updated: Sat Mar 16 11:18:14 2002
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