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    RE: iSCSI : default iSCSI mode page settings - Consensus call



    
    Bob,
    I think I agree with the direction of the note, but need to be sure we are
    on the same (mode) page:-)
    
    If you are saying the some values that effect an LU should be in LU
    specific Mode Pages, then fine in theory.  I just need to understand which
    ones you are referring to.  Since many of the Session parameters must be
    applied at the Transport, we need to know which iSCSI negotiated values you
    feel should be in the LU specific mode pages?  Or did I miss understand you
    statements?
    .
    .
    .
    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
    Internet address: hufferd@us.ibm.com
    
    
    Robert Snively <rsnively@Brocade.COM>@ece.cmu.edu on 10/02/2001 08:36:18 AM
    
    Sent by:  owner-ips@ece.cmu.edu
    
    
    To:   ips@ece.cmu.edu
    cc:
    Subject:  RE: iSCSI : default iSCSI mode page settings - Consensus call
    
    
    
    Folks,
    
    In an offline discussion, we have picked at a thread
    central to this fabric.  That is basically the view that
    one has of the structure of targets.
    
    ------------------   Note sent out a day ago  ---------------
    
    Traditional network environments talk from one big host
    memory to another big host memory.  In the storage space, the
    memory in the target is actually distributed between whatever
    caching and preprocessing space the target platform may have
    and the space held by each logical unit.  In some cases (RAIDs)
    the distribution is heavily in favor of the target platform
    cache.  In others (tapes), individual logical units may have
    100s of Megabytes of buffering which are not available to other
    logical units.  If you have mixed types of logical units or
    if you have the memory distributed unevenly among the logical
    units, different values are normal among different LUs.
    
    Different sessions to the same LU may also have different
    properties.  In particular, the LU may give away resources
    freely for the first few sessions, but more sparingly for
    subsequent sessions.  Alternatively, the LU may share the
    resources dynamically, providing UNIT ATTENTION indications
    if it must change the values.
    
    The iSCSI target is merely a handy portal to the logical
    units and device servers, which really run the show.  While
    many targets are simplified, sharing parameters across LUs
    and sessions, there is no requirement for that.  Sophisticated
    devices may have individual parameters for each LU and
    session.  iSCSI is trying hard to ignore the differences
    between storage and networking devices, but the differences
    are justified and genuine.
    
    ----------------   Some of the questions that triggered the note  -----
    
    > Are you saying that these parameters need to be able to have different
    > values for each LU among several LUs of single target in a single
    > session?
    >
    > Also would different sessions to the same LU all need to use the same
    > value?
    
    ---------------  And a succinct summary of the thoughts  ---------------
    
    If I understand correctly, in your view, such parameter negotiations
    should be per initiator and per LU.  Parameters which are unique per
    logical unit can be set (or "negotiated") *only* via mode pages.
    Whether or not changing the value for one logical unit changes it for
    others would be target end implementer's choice, subject to appropriate
    parameter change notifications to the initiator(s).  The values
    negotiated during login would be per initiator and per target
    default/initial values to be used when per LU mode pages have not been
    subsequently modified by this initiator.
    
    I am not reading that you think these values should not be settable at
    the per session level.  Only that you believe there is a real need to be
    able to change them at the per LU level so that the per session values
    can be over-ridden for specific LUs.  Changing the value for one LU via
    the mode pages would not have to change it for other LUs in this session
    nor for other sessions to this LU.
    
    Is that about right?
    
    ---------  My answer would be yes  -------------------------------------
    
    
    
    


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Last updated: Wed Oct 03 13:17:22 2001
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