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    Re: iSCSI: draft 7: remove S bit and Status field from the Data-i



    
    I am sure we don't want to enter this. The sequencing rules are there to
    asure:
    
       that there is no deadlock (order of data must follow the order of
       commands)
       that the target command buffer does not overflow (MaxCmdSN) - this will
       eliminate an "unlimited number of immediate"
    
    Any additional rules will interfere with performance, multiplexing policy
    etc. and I see no great
    value in enforcing them (and enforcing means checking and that means
    expense).
    
    Julo
    
    Sandeep Joshi <sandeepj@research.bell-labs.com>@ece.cmu.edu on 26-08-2001
    00:11:39
    
    Please respond to Sandeep Joshi <sandeepj@research.bell-labs.com>
    
    Sent by:  owner-ips@ece.cmu.edu
    
    
    To:   Dave Sheehy <dbs@acropora.rose.agilent.com>
    cc:   IETF IP SAN Reflector <ips@ece.cmu.edu>
    Subject:  Re: iSCSI: draft 7: remove S bit and Status field from the Data-i
    
    
    
    
    Julian,
    
    I wonder if Dave's last paragraph in this email has been considered.
    Here it is again..
    
    > This does help some. It eliminates the situation where a target can
    receive
    > an essentially unlimited number of immediate data commands prior to
    receiving
    > *any* data PDUs.
    
    in reference to Section 1.2.5
    > Unsolicited data MUST be sent on
    > every connection in the same order in which commands were sent.
    
    The draft currently allows
       c-1,c-2,c-3, (SEP-1-1),(SEP-1-2),(SEP-2-1,SEP-2-2),..
    where c-N = command {N}
    and   SEP-N-M = unsolicited (non-immediate) PDU number {M} for command
    {N}
    
    It would be simplify target login (ITT lookup) if we only permitted
    this sequence.
       c-1, SEP-1-1, SEP-1-2, c-2, SEP-2-1, SEP-2-2,..
    
    -Sandeep
    
    
    Dave Sheehy wrote:
    >
    > David,
    >
    > > I think you've taken a wrong turn.
    >
    > I think John hit the nail on the head.
    >
    > > > Second, thoughts of removing the immediate data seem not to be
    > > > simplification, since all the information to tie the data to the
    command
    > > is
    > > > right there with the command.  That has got to be easier than
    matching up
    > > > separate PDUs of data with the appropriate commands.
    > >
    > > Actually, that was the point, since the logic for "matching up separate
    > > PDUs of data with the appropriate commands" has to exist for inbound
    > > Data PDUs already.
    >
    > Except that there is a target context present in the solicited case to
    route
    > the data. That doesn't exist in the unsolicited case.
    >
    > > The slide I presented in London was about replacing
    > > immediate data with an unsolicited data PDU immediately following the
    > > command, thus removing the immediate data case in favor of reusing the
    > > logic for dealing with separate Data PDUs.  Remember that this was
    presented
    > > as a simplification possibility.
    >
    > This does help some. It eliminates the situation where a target can
    receive
    > an essentially unlimited number of immediate data commands prior to
    receiving
    > *any* data PDUs.
    >
    > But, do you mean to say that *one* unsolicited data PDU would follow the
    > command? Wouldn't that be unnecessarily restrictive if the PDU size is
    small?
    > Simply guaranteeing that the data PDUs will immediately follow the
    command
    > seems like an adequate improvement.
    >
    > Dave Sheehy
    
    
    
    


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Last updated: Tue Sep 04 01:03:54 2001
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