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    Re: iSCSI: Login Redirect



    Title:
    Caitlin Bestler wrote:
    On Tuesday, July 15, 2003, gilligan@intransa.com wrote:
    
      
    Hi - If you are using redirect to implement fault
    tolerance/load balancing as we sketched out in
    draft-gilligan-iscsi-fault-tolerance-00.txt, there may be
    transients when an initiator gets  redirected multiple times. 
    For example, say A redirects the initiator to B.  But say B has
    more recent information about the actual location of the
    target, so it redirects the initiator to C.  Eventually A
    learns the same information as B and then redirects initiators
    directly to C.  So the initiator should be prepared to accept
    some number of consecutive redirects.
    
    Of course, if the redirection goes on indefinitely or loops - say A 
    redirects to B, which redirects to C, which redirects to A, etc. - that 
    probably does represent either a configuration error or a bug.  So the 
    initiator may wish to detect a redirection loop or an excessive number 
    of  redirections.
    
    But, as you point out, what represents "excessive redirection"
    is in the eye of the initiator.  So, I don't think that the
    main iSCSI spec needs to call out a specific hard limit.
    
        
    
    In order to cover the type of fault-tolerance scenario you cited
    wouldn't it make sense to set a minimum that the initiator SHOULD
    be willing to accept?
    
    That way cluster builders would have a base that they could assume
    would not result in iniator failures (only delays).

    Yes, it would be good to have some sort of minimal redirect/retry behavior specified, but I'm not sure that it necessarily needs to be specificied in terms of a minimun number of redirects to accept.  It might be more natural to define it in terms of time:  how long an initiator should try to login to a target (in the face of multiple redirects) before giving up and notifying the upper layer.  However it is implemented, it would also be desirable for the initiator to make this count or interval configurable so that it can be tuned for use in different environments.

    Bob.
      



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Last updated: Tue Aug 05 12:46:12 2003
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