On 07/07/2011 04:37 PM, SR wrote:
> Hi,
> If I have following negotiated parameters for iscsi read command then
> are following explained scenarios possible (I wasn't sure about
> scenario-1) ?
> MaxBurstLength = 128K
> FirstBurstLength = 32K

For reads FirstBurstLength does not come into play. It is just for
writes and immediate data and initial r2t handling.

> MaxRecvDataSegmentLength = 8K
> SCSI (read) command PDU specifies total data length = 25K
> Which scenario out of following two should be considered is correct
> operation? Is scenario-1 possible?
> What are the main factors taken into account before chopping SCSI data
> into iSCSI PDU?
> Scenario-1:
> iSCSI Data-In PDUs:
> PDU1 with data length=4K
> PDU2 with data length=4K
> PDU3 with data length=4K
> PDU4 with data length=4K
> PDU5 with data length=4K
> PDU6 with data length=4K
> PDU7 with data length=1K

I think the iscsi RFC just says that the target cannot send more than
MaxRecvDataSegmentLength bytes, so it is valid for it to send PDUs with
only 4K.

> Scenario-2:
> iSCSI Data-In PDUs:
> PDU1 with data length=8K
> PDU2 with data length=8K
> PDU3 with data length=8K
> PDU4 with data length=1K

I think this is more common.

> Can you point me to the code where this decision is made about
> chopping SCSI data into iSCSI PDU.

The initiator does not do the chopping for READs. The target does this.
We just read in whatever the target sends us.

For WRITEs there is iscsi_prep_scsi_cmd_pdu and

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