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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: iSCSI: data and data sequences for ReadPaul, Nothing limits the burst rate except the TCP window. The bursts for read accomplish several things: they might be good "turnaround" points for bi-directional commands (minor) they delimit data that can be (on request) positive ack-ed enabling resources to be released at target Julo Paul Koning <ni1d@arrl.net> Sent by: owner-ips@ece.cmu.edu 14-11-01 00:22 Please respond to Paul Koning To: ips@ece.cmu.edu cc: Subject: iSCSI: data and data sequences for Read I hope this isn't a dumb question, but between the -08 spec and the archives I'm puzzled about the details around data sequences in the case of Read operations. As far as I can tell, a read can result in one or more data sequences coming back. These are numbered with DataSN values that keep going up across sequence boundaries. Each sequence is limited by MaxBurstSize, but the total Read size (sum of all the sequences) is not bounded other than by SCSI. In the Write case, something analogous happens but there there's an R2T to control the flow of data sequences. As far as I can see, there is nothing analogous in the Read case. In other words, while MaxBurstSize limits the size of a data sequence, there is no mechanism limiting the number of bursts, or the rate at which you send back DatIn PDUs (other than TCP window control). Is that right or did I miss something? If it's right, what is the purpose of having the notion of a Data Sequence for DataIn, and what does MaxBurstSize do for you in that case? Thanks, paul
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