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    iSCSI: unsolicited data



    Julian,
    
    I don't recall the earlier discussion being conclusive on this topic,
    so let me attempt to make a couple of suggestions on this.
    
    Last para in Section 2.2.5 (page 33) in rev09 mandates unsolicited
    data ordering with the following wording.  
     
      "iSCSI initiators and targets MUST also enforce some ordering rules to
       achieve deadlock-free operation. Unsolicited data MUST be sent on
       every connection in the same order in which commands were sent. A
       target receiving data out of order SHOULD terminate the session."
    
    I have a couple of suggestions to reword -
    
    - The reference to a deadlock is true only for an implementation 
      overcommitting the unsolicited data buffers.  So, I would suggest 
      dropping this reasoning. 
    
    - The "MUST enforce"  wording should also add that "targets MAY 
      however see unexpected unsolicited data (UUD), following data 
      digest errors on expected unsolicited data."
    
    - Finally, the "SHOULD terminate the session", IMHO, is too strong.
      This wording will imply that a session is vulnerable to a single 
      digest error regardless of recovery level.  [ I however disfavor 
      attaching more assorted semantics to recovery levels (than the 
      current easily understood "level = setof(recovery classes)"
      formulation). ]  As you mentioned on this discussion earlier, a 
      UUD is a protocol error (or may be not, if it is the effect of 
      a prior digest failure).  
    
      We can choose to Reject ("protocol error") the UUD and discard the 
      data.  The only problem with this approach is: following a digest
      error on unsolicited data for one task, all the following unsolicited
      data in flight would have to be discarded.  One option is to imply
      that the target update the "expected unsolicited data"  so the 
      unsolicited data following in the pipe can be processed normally.
      So, I guess it would be saying: "the target MAY Reject the UUD".
        
    Comments?
    -- 
    Mallikarjun 
    
    
    Mallikarjun Chadalapaka
    Networked Storage Architecture
    Network Storage Solutions Organization
    MS 5668	Hewlett-Packard, Roseville.
    cbm@rose.hp.com
    


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Last updated: Mon Dec 03 13:17:46 2001
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