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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: iscsi : Fragmentation & Reassembly issues in iSCSI.Santosh, The intent was to enable lower limits for ping and text. I would be reluctant to use the same limit as in some contexts the PDU limit could be practically very large. PDU will be limited at first by 2 factors - the CRC and the need to limit loss-of-framing temporary memory. If and when the underlying transport will have a good RDMA mechanism and we will have a decent CRC-64 or we are using IPsec the PDU limit could be extremely large. We don't want the same to hold for Ping, Text etc. However we would like to have the PDU limit to hold for all as it is mainly meant for framing and CRC. For all those reasons I suggest limiting the text length also to the lower of the two. Julo Santosh Rao <santoshr@cup.hp.com> on 19/01/2001 23:59:49 Please respond to Santosh Rao <santoshr@cup.hp.com> To: Julian Satran/Haifa/IBM@IBMIL, ips@ece.cmu.edu cc: Subject: Re: iscsi : Fragmentation & Reassembly issues in iSCSI. julian_satran@il.ibm.com wrote: > <js> I will introduce in 04 a statement saying that that PingMaxRelayLength > will be limited by the lowest of the two </js> Julian, The fragmentation issue as explained in the above example is also applicable for the Login and Text Commands. (TotalText > DataPDULength). In the case of these commands, a "F" bit is required in bit 7 of byte 1 of the command & response PDUs to indicate the last command or response PDU due to the fragmentation issues that arise from TotalText & DataPDULength. > Solution : > ======= > Specify explicitly in Appendix C that DataPDULength is only applicable > for SCSI Command PDU and SCSI Data PDU. The current definition is open > to being mis-interpreted as a form of iSCSI MTU, something that can > result in the iSCSI layer having to deal with fragmentation and > re-assembly issues for non-SCSI PDUs. > > <js> What would be those? Text commands? Login? Nops? Having a single limit > seemms simpler </js> On the lines of your above solution, (based on a single limit), removal of PingMaxReplyLength should be considered and implicitly use DataPDULength as the PingMaxReplyLength. This ensures only 1 limit for NOP-OUT/NOP-IN. Regards, Santosh
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