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    Re: iSCSI:Request/Response Ordering



    The simple answer is that an initiator may not make any assumptions about
    the order of requests to the same blocks (by itself or other initiators)
    that may be outstanding at the same time.  If you care about ordering, an
    initiator must wait until previous requests are complete before issuing a
    request that references the same block(s).
    
    This assumes that all commands are issued as simple tasks, which is the most
    common situation today (one suspects the only situation).
    
    People have suggested more complex schemes in the past, amounting to
    exporting some portion of the transfer dependency graph to the target.  The
    ordered task attribute is one approach to this.  None have proved practical
    in practice.
    
    In practice, if a target receives references to the same block from multiple
    initiators, it can perform the operations in whatever order it wishes.
    There is no "correct" order, all are equally valid.  (Again, I'm assuming
    all are issued as simple tasks).
    
    Edward A. Gardner               eag@ophidian.com
    Ophidian Designs                719 593-8866 voice
    1262 Hofstead Terrace           719 593-8989 fax
    Colorado Springs, CO  80907     719 210-7200 cell
    -----Original Message-----
    From: Sanjeev Bhagat (TRIPACE/Zoetermeer) <iscsi_t10@sanjeevbhagat.com>
    To: 'IPS Reflector' <ips@ece.cmu.edu>; T10@t10.org <T10@t10.org>
    Date: Saturday, September 29, 2001 7:03 PM
    Subject: iSCSI:Request/Response Ordering
    
    
    Hello All (T10, IPS),
    
    The SAM-2 specifications makes no assumption about, or places any
    requirement on the ordering of requests or responses between tasks or task
    management functions received from different SCSI initiator ports.
    
    In this scenario how can a SCSI target make correctly handle the read/write
    requests made on same blocks by different intiators at the same time.
    
    Sanjeev
    
    
    
    


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Last updated: Sun Sep 30 07:17:26 2001
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