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    RE: iSCSI: problem with LUN discovery



    > -----Original Message-----
    > From: owner-ips@ece.cmu.edu [mailto:owner-ips@ece.cmu.edu]On Behalf Of
    > John Hufferd/San Jose/IBM
    > Y P Cheng,
    > OK, now I have detected an important communication problem here.  What you
    > are calling a LUN is not what the rest of us folks (or at lest me) call a
    > LUN.  <snip> <snip>
    
    Thank you for a nice summary of the definitions of LU and LUN.  No, we did
    not have disagreement.  It is only mis-communication.  (If I did not real
    your email incorrectly.)
    
    LUN, the address of an LU, is embedded in an iSCSI command PDU or an FC
    command frame to direct a SCSI command to the LU.  What confuses people is
    that the SCSI LU today is virtual and has nothing to do with real physical
    devices.  The virtual to real mapping will be done by system administrator
    who reconfigures new and replaces bad SCSI devices.  Each SCSI device in
    iSCSI should have a GUID.  However, a physical device is not visible to an
    application. Software like Veritas adds one more layer of virtualization by
    taking the virtual LU's and making them virtual volumes.
    
    All I said was that the LUN needs not be unique world wide.  An LU has its
    unique attributes that can be obtained by page 0x83h.  A login or CONNECT
    discussed in another thread provides the TCP connection to reach an iSCSI
    node.  The connection is used by the TCP/IP transport.  Within an iSCSI PDU,
    an LUN is specified.
    
    


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Last updated: Tue Sep 04 01:06:48 2001
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