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
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