Bart Van Assche wrote: > On Feb 5, 2008 6:01 PM, Erez Zilber <erezz@xxxxxxxxxxxx> wrote: > >> Using such large values for FirstBurstLength will give you poor >> performance numbers for WRITE commands (with iSER). FirstBurstLength >> means how much data should you send as unsolicited data (i.e. without >> RDMA). It means that your WRITE commands were sent without RDMA. >> > > Sorry, but I'm afraid you got this wrong. When the iSER transport is > used instead of TCP, all data is sent via RDMA, including unsolicited > data. If you have look at the iSER implementation in the Linux kernel > (source files under drivers/infiniband/ulp/iser), you will see that > all data is transferred via RDMA and not via TCP/IP. > > When you execute WRITE commands with iSCSI, it works like this: EDTL (Expected data length) - the data length of your command FirstBurstLength - the length of data that will be sent as unsolicited data (i.e. as immediate data with the SCSI command and as unsolicited data-out PDUs) If you use a high value for FirstBurstLength, all (or most) of your data will be sent as unsolicited data-out PDUs. These PDUs don't use the RDMA engine, so you miss the advantage of IB. If you use a lower value for FirstBurstLength, EDTL - FirstBurstLength bytes will be sent as solicited data-out PDUs. With iSER, solicited data-out PDUs are RDMA operations. I hope that I'm more clear now. Erez - To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
