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    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: Wed Nov 14 09:17:44 2001
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