SORT BY:

LIST ORDER
THREAD
AUTHOR
SUBJECT


SEARCH

IPS HOME


    [Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

    RE: iSCSI: changing MaxPDUDataLength



    Mallikarjun,
    
    	I had tracked your earlier comments, I was just responding to Eddy's
    concern that there is a need for a "good time" from the target's
    perspective and saying I don't believe quiescing the connection would
    be an issue from an initiator's perspective. I still don't, I think
    the imitator has enough tools to avoid quiescing a connection if it
    believes that to be a bad thing.
    
    	- Rod
    
    -----Original Message-----
    From: owner-ips@ece.cmu.edu [mailto:owner-ips@ece.cmu.edu]On Behalf Of
    Mallikarjun C.
    Sent: Wednesday, June 12, 2002 12:58 PM
    To: Rod Harrison
    Cc: ips@ece.cmu.edu
    Subject: Re: iSCSI: changing MaxPDUDataLength
    
    
    Rod,
    
    If you had tracked my earlier comments, you'd notice that
    I'm arguing that there's no specific reason for a "good time".
    Certain hardware implementations may choose to effect the
    change only on Data-In sequence boundaries, but the basic
    nature of text negotiation allows for that flexibility.
    
    Yes, as you suggest, we have a variety of other options including
    dropping the I/Os, or the connection etc.  But the point in allowing
    dynamic redeclaration of this key is to make iSCSI adapt to
    but not be impacted by, lower-level dynamics - similar to TCP.
    --
    Mallikarjun
    
    Mallikarjun Chadalapaka
    Networked Storage Architecture
    Network Storage Solutions
    Hewlett-Packard MS 5668
    Roseville CA 95747
    cbm@rose.hp.com
    
    
    ----- Original Message -----
    From: "Rod Harrison" <rod.harrison@windriver.com>
    To: "Mallikarjun C." <cbm@rose.hp.com>; "Eddy Quicksall"
    <eddy_quicksall@ivivity.com>; "Julian Satran"
    <Julian_Satran@il.ibm.com>
    Cc: <ips@ece.cmu.edu>
    Sent: Tuesday, June 11, 2002 4:15 PM
    Subject: RE: iSCSI: changing MaxPDUDataLength
    
    
    > Mallikarjun ,
    >
    > The current wording doesn't appear to prevent the initiator from
    > staging new commands whilst the negotiation is in process and
    > therefore the target may never find a "good time" to end the
    > negotiation sequence.
    >
    > I don't think idling the connection would be a big issue in the
    event
    > of  PMTU change since the worst case is that existing commands have
    to
    > run to completion using the inefficient PMTU. The initiator also has
    > the options of aborting and restarting the commands if they can't
    > complete with the old PMTU, or better, open another connection with
    > the appropriate MaxPDUDataLength and change the command allegiance.
    >
    > - Rod
    >
    > -----Original Message-----
    > From: owner-ips@ece.cmu.edu [mailto:owner-ips@ece.cmu.edu]On Behalf
    Of
    > Mallikarjun C.
    > Sent: Tuesday, June 11, 2002 2:35 PM
    > To: Eddy Quicksall; Julian Satran
    > Cc: ips@ece.cmu.edu
    > Subject: Re: iSCSI: changing MaxPDUDataLength
    >
    >
    > Eddy,
    >
    > I am not clear on why you think the target code becomes messy on
    > a PDU size change.  The last para in section 4.4 states the
    > following -
    >
    > "Parameters negotiated by a text exchange negotiation sequence
    become
    > effective only after the negotiation sequence is completed."
    >
    > Since the target gets to complete a text negotiation with a Text
    > Response
    > PDU, it can time the applicability of a changed
    > MaxRecvDataSegmentLength.
    >
    > Requiring that an initiator must idle the connection before changing
    > this
    > parameter, IMHO, is counter-productive when there's a dynamic PMTU
    > degradation in the presence of long-running commands (writes in
    > particular).
    > Once the initiator starts the renegotiation, target would ideally
    want
    > to quickly
    > renegotiate its receive size as well to receive ULPDU-contained
    > segments.
    >
    > In short, seems to me that the draft is saying what you would like.
    > --
    > Mallikarjun
    >
    > Mallikarjun Chadalapaka
    > Networked Storage Architecture
    > Network Storage Solutions
    > Hewlett-Packard MS 5668
    > Roseville CA 95747
    > cbm@rose.hp.com
    >
    >
    > ----- Original Message -----
    > From: "Eddy Quicksall" <eddy_quicksall@ivivity.com>
    > To: "Julian Satran" <Julian_Satran@il.ibm.com>
    > Cc: <ips@ece.cmu.edu>
    > Sent: Tuesday, June 11, 2002 7:56 AM
    > Subject: RE: iSCSI: changing MaxPDUDataLength
    >
    >
    > > I think it should be a requirement because if it is not, all
    target
    > code
    > > will have to have the messy code. Or, we could say that if it is
    not
    > idle
    > > commands, then the target may reject it.
    > >
    > > Eddy
    > >
    > > -----Original Message-----
    > > From: Julian Satran [mailto:Julian_Satran@il.ibm.com]
    > > Sent: Tuesday, June 11, 2002 9:11 AM
    > > To: Eddy Quicksall
    > > Cc: ips@ece.cmu.edu; pat_thaler@agilent.com
    > > Subject: RE: iSCSI: changing MaxPDUDataLength
    > >
    > >
    > >
    > > That is a fair request - we may slip in a recommendation to that
    > effect (in
    > > chapter 11?)
    > >
    > > Julo
    > >
    > >
    > >
    > > Eddy Quicksall <eddy_quicksall@ivivity.com>
    > >
    > >
    > > 06/11/2002 04:28 AM
    > > Please respond to Eddy Quicksall
    > >
    > >
    > >
    > >         To:        Julian Satran/Haifa/IBM@IBMIL
    > >         cc:        ips@ece.cmu.edu, pat_thaler@agilent.com
    > >         Subject:        RE: iSCSI: changing MaxPDUDataLength
    > >
    > >
    > >
    > >
    > > How about if we say that an initiator must not change the
    > MaxPDUDataSize
    > > unless it first idles the commands (at least the ones with the R
    > bit) or if
    > > ErrorRecoveryLevel==0?
    > >
    > > That would simplify target code greatly and would meet the design
    > goals; and
    > > since it should be rare to change it, it would be of little impact
    > to idle
    > > the commands for a split second.
    > >
    > >
    > > Eddy
    > > -----Original Message-----
    > > From: Julian Satran [mailto:Julian_Satran@il.ibm.com]
    > > Sent: Monday, June 10, 2002 8:06 PM
    > > To: Eddy Quicksall
    > > Cc: ips@ece.cmu.edu; pat_thaler@agilent.com
    > > Subject: RE: iSCSI: changing MaxPDUDataLength
    > >
    > >
    > > I said only that when you change length you can ask for all PDUs
    > after the
    > > ack! (no need to keep a tall - the old offsets are good up to the
    > hole).
    > >
    > > Julo
    > >
    > >
    > > Eddy Quicksall <eddy_quicksall@ivivity.com>
    > >
    > >
    > > 06/11/2002 12:32 AM
    > > Please respond to Eddy Quicksall
    > >
    > >
    > >        To:        Julian Satran/Haifa/IBM@IBMIL
    > >        cc:        ips@ece.cmu.edu, pat_thaler@agilent.com
    > >        Subject:        RE: iSCSI: changing MaxPDUDataLength
    > >
    > >
    > >
    > >
    > >
    > > Julian,
    > >
    > > Another problem here is that the target has to calculate the
    offset
    > from the
    > > DataSN #. And as BegRun can be any value. E.g., BegRun=4 and
    > RunLngth=0
    > > means starting DataSN=4, send all the data for that sequence.
    > >
    > > I think it would be a performance hit and waist of memory to keep
    a
    > tally of
    > > all PDU sizes just for an occasional SNACK.
    > >
    > > It's not that it can't be done ... it is more that it is messy and
    I
    > think
    > > there is a solution that will satisfy the design requirements but
    > keep the
    > > software simpler.
    > >
    > > Eddy
    > > -----Original Message-----
    > > From: Julian Satran [mailto:Julian_Satran@il.ibm.com]
    > > Sent: Saturday, June 08, 2002 10:16 PM
    > > To: Eddy Quicksall
    > > Cc: ips@ece.cmu.edu; owner-ips@ece.cmu.edu; pat_thaler@agilent.com
    > > Subject: RE: iSCSI: changing MaxPDUDataLength
    > >
    > >
    > > That is not completely accurate.
    > > The only problem is when PDU size decreases and then SNACK must be
    > for all
    > > data.
    > > Target can also keep a mapping of numbers/to offsets (the list
    > should be
    > > small and if it gets long ask for ack (A-bit).
    > >
    > > Julo
    > >
    > > Eddy Quicksall <eddy_quicksall@ivivity.com>
    > > Sent by: owner-ips@ece.cmu.edu
    > >
    > >
    > > 06/08/2002 10:54 PM
    > > Please respond to Eddy Quicksall
    > >
    > >
    > >       To:        pat_thaler@agilent.com
    > >       cc:        ips@ece.cmu.edu
    > >       Subject:        RE: iSCSI: changing MaxPDUDataLength
    > >
    > >
    > >
    > >
    > >
    > >
    > > Thanks,
    > >
    > > As a target, I won't be able to let it change until all of the
    > outstanding
    > > commands are finished (running with ErrorRecoveryLevel>=1). This
    is
    > because
    > > I must use the PDU size to compute the offset from a SNACK's
    > > BegRun/RunLength.
    > >
    > > So, I plan to not give the text response for a
    MaxPDURecvDataLength
    > in FFP
    > > until I get back an ExpStatSN == next StatSN.
    > >
    > > This will cause a delay of unknown time before the PDU size can
    > actually
    > > change ... do you see any problem with this?
    > >
    > > Eddy
    > >
    > > -----Original Message-----
    > > From: pat_thaler@agilent.com [mailto:pat_thaler@agilent.com]
    > > Sent: Friday, June 07, 2002 1:13 PM
    > > To: eddy_quicksall@ivivity.com; ips@ece.cmu.edu
    > > Subject: RE: iSCSI: changing MaxPDUDataLength
    > >
    > >
    > > Eddy,
    > >
    > > If one uses a message sync and steering that relys on the
    transport
    > segments
    > > carrying a full PDU, e.g. TCP ULP Framing Protocol (TUF), then if
    > the path
    > > MTU changes one would want to change the PDU data length to fit
    the
    > new path
    > > MTU.
    > >
    > > Pat
    > >
    > > -----Original Message-----
    > > From: Eddy Quicksall [mailto:eddy_quicksall@ivivity.com]
    > > Sent: Wednesday, June 05, 2002 12:24 PM
    > > To: ips@ece.cmu.edu
    > > Subject: iSCSI: changing MaxPDUDataLength
    > >
    > >
    > > Does anybody know a case where it is necessary to support a new
    PDU
    > data
    > > length during full feature phase?
    > >
    > > Eddy
    > > mailto: Eddy_Quicksall@iVivity.com
    > >
    > >
    > >
    > >
    > >
    > >
    > >
    > >
    >
    >
    
    


Home

Last updated: Wed Jun 12 16:18:40 2002
10712 messages in chronological order