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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: DataSegmentLength of 0Barry, OK - it reads: 1.1.1 DataSegmentLength This is the data payload length of a SCSI Data-In or SCSI Data-Out PDU; sending of 0 length data segments should be avoided, but initiators and targets must be able to properly receive 0 length data segments. Regards, Julo "Barry Reinhold" <bbrtrebia@mediaone.net> on 07-06-2001 17:06:19 Please respond to "Barry Reinhold" <bbrtrebia@mediaone.net> To: Julian Satran/Haifa/IBM@IBMIL cc: "Jon Sreekanth" <jon.sreekanth@trebia.com>, "James Smart" <james.smart@trebia.com> Subject: DataSegmentLength of 0 Julian, Clause 2.7.6, DataSegmentLength, States the following: "This is the data payload length of a SCSI Data-In or SCSI Data-Out PDU; sending of 0 length data segments should be avoided." For devices that are going to act as protocol translators between Fibre Channel and iSCSI it is going to be just about impossible not to send a data segment length of 0 if we get an underrun condition. (This happens on inquery responses. From the Fibre Channel side there is no way to tell that the data has been sent until you get a FCP_RSP. At this point the iSCSI data frames have already been sent with all the data, but the F bit still needs to be set. The translating device therefore needs to send a frame with a 0 length data segment and the F bit set.) Hence, I suspect almost all devices that are not acting as end points to IO operations will have this problem and you will see iSCSI data frames with the F bit set and the 0 length data segments. I agree that we don't want to send 0 length segments, but I do think we need to be able to handle them if they are generated. In order to make people aware of the need to handle 0 length frames I was looking for wording changes to the spec along these lines: "This is the data payload length of a SCSI Data-In or SCSI Data_Out PDU; sending of 0 length data segments should be avoided, but devices must be able to properly receive 0 length data segments." In this way it makes it clear that reception of 0 length data segments is required (which I think was the intent) and devices will be more likely to interoperate. Barry Reinhold Principal Architect Trebia Networks barry.reinhold@trebia.com 603-868-5144/603-659-0885/978-929-0830 x138
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