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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] RE: iscsi: unsolicited data questionNot exactly - an initiator may decide to send only non immediate or only immediate in the first case the absence of F is the sign of things to come and in the later F indicates nothing will come. The later is allowed. Julo
Thanks to yours and others' explanation, now I am more clear, but I have another question: Based on your reply, and let me emphasize it by repeating the 4th paragraph on page 42 of draft 12-98: "... If any non-immediate unsolicited data are sent, the total unsolicited data MUST be either the negotiated amount or all the data if the total amount is less than the negotiated amount for unsolicited data. ..." With this rule, do we still need the F bit in the Data-out (both for the solicited and unsolicited Data-out)? The F bit seems redundant since the target has enough information to figure out the final unsolicited Data-out and the final solicited Data-out (based on the FirstBurstSize, Offset and DataSegmentLength in the Data-out, and the ExpectedDataTransferLength in the corresponding SCSI Write PDU). Thanks, Dennis -----Original Message----- From: Julian Satran [mailto:Julian_Satran@il.ibm.com] Sent: Wednesday, June 12, 2002 11:21 AM To: Dennis Young Cc: ips@ece.cmu.edu; owner-ips@ece.cmu.edu Subject: RE: iscsi: unsolicited data question You are wrong about waiting - read my previous text. You need unsolicited as the amount in one PDU may not be all you want. Julo
Are you saying that, for a session that has InitialR2T=No in effect, the initiator must send all its data as unsolicited first, up to the amount negotiated in FirstBurstSize, before it waits for a R2T from the target? Can you shed some light on why we need unsolicited Data-out PDU when there is ImmediateData, seems like they both serve the same purpose, having both of them only make the spec more complex. Thanks, -Dennis -----Original Message----- From: Julian Satran [mailto:Julian_Satran@il.ibm.com] Sent: Wednesday, June 12, 2002 10:19 AM To: Dennis Young Cc: ips@ece.cmu.edu; owner-ips@ece.cmu.edu Subject: RE: iscsi: unsolicited data question This is the reason why the initiator is required to send ALL unsolicited data (target can count on it and start sending R2Ts as soon as it sees the first header> Neither bandwidth nor latency are wasted. Julo
Julian, This leads me to a more interesting question. A session with InitialR2T=No in effect, i.e. unsolicited Data-out allowed, could cause unintended waste of bandwidth, depending on how fast the target sends our R2T in response to the SCSI Write. If the target sees the unsolicited Data-out PDU before building the R2T, then everything is fine. If the target doesn't see the unsolicited Data-out PDU before building the R2T, the R2T would request the same portion of data in the unsolicited Data-out, thus bandwidth is wasted. The question is, how can a target be smart about this? Should the target wait a moment for the possible unsolicited Data-out after receiving each SCSI Write, this sounds kludgy. Also, why do we need the unsolicited Data-out PDU feature when there is ImmediateData? Regards, Dennis -----Original Message----- From: Julian Satran [mailto:Julian_Satran@il.ibm.com] Sent: Wednesday, June 12, 2002 6:05 AM To: Dennis Young Cc: ips@ece.cmu.edu; owner-ips@ece.cmu.edu Subject: Re: iscsi: unsolicited data question yes - julo
I have a question which has been asked before, but I couldn't find a direct answer in the archive. The table on page 200 of draft 12 doesn't directly answer this question either. The first paragraph on page 36 of draft 12 says "Targets operate in either solicitied (R2T) data mode or unsolicited (non R2T) data mode." tells me that a target, at all times during a data sequence transfer, can be one or the other, but not both (non R2T for the initial data out, R2T for the remaining data). Is this correct? Thanks, Dennis ---snip from an old email dated 3/30/2001--- " Hi Julian Sorry if I'm covering old ground... Is it possible to use unsolicited data for the first burst and then request any remaining data using R2T? For example, if the target has a previously allocated buffer available (length defined by FirstBurstSize) for unsolicited data, then once the initiator has sent unsolicited data up to and including this amount then the remaining data (if any) can be requested using R2T once the target has the buffer space available. ...Matthew Burbridge Hewlett Packard, Bristol Telnet: 312 7010 E-mail: matthewb@bri.hp.com "
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