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    RE: iSCSI: update on OOO CmdSNs/connection



    Somesh,
    
    Read further - yes it is back a MUST (it does not make sense to make it a 
    blanket SHOULD).
    
    Julo
    
    
    
    
    "Somesh Gupta" <somesh_gupta@silverbacksystems.com>
    Sent by: owner-ips@ece.cmu.edu
    15-11-01 20:54
    Please respond to somesh_gupta
    
     
            To:     <ips@ece.cmu.edu>
            cc: 
            Subject:        RE: iSCSI: update on OOO CmdSNs/connection
    
     
    
    Julian,
    
    As was mentioned previously, there is a signficant
    different in how you design for error recovery
    corner cases, and how you design for the main path.
    
    The SHOULD is neither. I would prefer one of the following
    
    1. Make it a MUST or not mention it at all.
    or
    2. Make it a negotiable parameter.
    
    The way it is, it does not provide any benefit to
    the initiator (it is a MUST in a very important case),
    and for the target it becomes a nebulous design choice.
    
    Regards,
    Somesh
    
    > -----Original Message-----
    > From: owner-ips@ece.cmu.edu [mailto:owner-ips@ece.cmu.edu]On Behalf Of
    > Julian Satran
    > Sent: Wednesday, November 14, 2001 5:46 AM
    > To: ips@ece.cmu.edu
    > Subject: RE: iSCSI: update on OOO CmdSNs/connection
    >
    >
    > Somesh,
    >
    > The reason we have put in the SHOULD is that it better reflects what is
    > happening on recovery anyhow.
    > The text also clearly outlines when the SHOULD becomes MUST and that is
    > the case you where concerned about.
    >
    > Regards,
    > Julo
    >
    >
    >
    >
    >
    > "Somesh Gupta" <somesh_gupta@silverbacksystems.com>
    > Sent by: owner-ips@ece.cmu.edu
    > 13-11-01 22:53
    > Please respond to somesh_gupta
    >
    >
    >         To:     "ips" <ips@ece.cmu.edu>
    >         cc:
    >         Subject:        RE: iSCSI: update on OOO CmdSNs/connection
    >
    >
    >
    > Julian,
    >
    > I am surprised to see the text in the latest rev
    > of the doc change as suggested by Mallikarjun.
    > I did not think there was a consensus on this
    > subject.
    >
    > Just because I did not respond to Mallikarjun's
    > last comment publicly should not be construed
    > as agreement. Having the last word is hopefully
    > not assumed to be consensus, otherwise a thread
    > may never end.
    >
    > Somesh
    >
    > > -----Original Message-----
    > > From: owner-ips@ece.cmu.edu [mailto:owner-ips@ece.cmu.edu]On Behalf Of
    > > Somesh Gupta
    > > Sent: Friday, November 09, 2001 3:26 PM
    > > To: ips
    > > Subject: RE: iSCSI: update on OOO CmdSNs/connection
    > >
    > >
    > > Mallikarjun,
    > >
    > > I never liked the SHOULD. It is not a design point.
    > > If we really want to allow it, perhaps a negotiation
    > > parameter is a better choice (which is only
    > > marginally better). Error detection and recovery
    > > have completely different design requirements than
    > > the data path.
    > >
    > > So ideally we say MUST or nothing
    > > or we negotiate it
    > >
    > > Also on your point A, it "MUST" be a MUST on
    > > a single connection case except for when required
    > > for error recovery (i.e. the very very rare -
    > > case of digest error).
    > >
    > > Somesh
    > >
    > > > -----Original Message-----
    > > > From: owner-ips@ece.cmu.edu [mailto:owner-ips@ece.cmu.edu]On Behalf 
    Of
    > > > Mallikarjun C.
    > > > Sent: Friday, November 09, 2001 1:49 PM
    > > > To: ips
    > > > Subject: iSCSI: update on OOO CmdSNs/connection
    > > >
    > > >
    > > > To those interested in this discussion:
    > > >
    > > > Julian and I had a phone conversation on the topic
    > > > of OOO CmdSNs on a connection.  An update follows.
    > > >
    > > > Julian agrees that there are valid error recovery
    > > > scenarios where CmdSNs will legitimately end up OOO
    > > > on a given connection.
    > > >
    > > > OTOH, I agree with two of Julian's scenarios that he
    > > > pointed out right away - the "cleaning command" (command
    > > > required to be sent after a retry copy to ensure flushing
    > > > within 2^31 -1), and an immediate Logout posted with
    > > > unacknowledged commands.  Neither of this can be shipped
    > > > OOO - since the former undoes the flushing intent, and
    > > > the latter breaks the rule that nothing more follows a
    > > > Logout on the connection (and troublesome in other ways,
    > > > see below).
    > > >
    > > > In general, I share the concern with Julian that we
    > > > have not closely scrutinized all possibilities.
    > > >
    > > > With that said, something along the following lines
    > > > seemed reasonable -
    > > >
    > > > A)Initiator MUST send commands in increasing order of
    > > >   CmdSN on a connection if both the following are true -
    > > >              - operational ErrorRecoveryLevel is 0,
    > > >              - MaxConnections is negotiated to 1.
    > > > B)In all the other cases, initiator SHOULD send commands
    > > >   in increasing order of CmdSN on a connection.  It is
    > > >   strongly encouraged that commands with out-of-order
    > > >   CmdSNs be sent on a connection only if they are
    > > >   retransmitted commands due to digest error recovery
    > > >   and connection recovery.
    > > >
    > > > I also suggest the following upon further reflection-
    > > >
    > > > C)Add wording in section 2.2.2.1 to mandate that
    > > >   the cleaning command MUST be sent in-order after
    > > >   the retried command.
    > > > D)Warn clearly that sending an immediate Logout command
    > > >   in the presence of other unacknowledged commands MAY
    > > >   create inadvertent discarding of certain commands (even
    > > >   if it is a recovery Logout), and MAY cause protocol
    > > >   errors leading to ungraceful shutdown of the connection.
    > > >
    > > > Hopefully A will bring the determinism that Somesh was
    > > > looking for certain design points.  B describes the more
    > > > general n-connection session case.  C & D are fixes for
    > > > two identfied areas (so far) which will break.
    > > >
    > > > 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: Fri Nov 16 00:18:07 2001
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