|
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] RE: iSCSI: changing MaxPDUDataLengthMallikarjun, 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 |