Re: iSCSI SCSI command F bit questions

[wrstuden@wasabisystems.com]

On Tue, 8 Apr 2003 AClarke@attotech.com wrote:

> I have a few questions about iSCSI data transfer.
>
> In section 10.3.1 of the spec describing the F bit, why is the word "may"
> used?  I think that when Expected Data Transfer Length is larger than
> DataSegmentLength the target "MUST" solicit the additional data.  Is there
> a situation when the target should not send an R2T for the rest of the
> data?

Note, that's "may", not "MAY". It's a polite phrasing. It means it's up to
the target to get the rest of the data.

> Is it at the initiator's discretion to set this bit, even if InitialR2T=No,
> ImmediateData=Yes, and DataSegmentLength is less than FirstBurstLength?

Kinda. In the case you describe, it is at the initiator's discression what
kind of unsolicited data transmission it wants to do. But given a decision
(no unsolicited, unsolicited burst, immediate data, immediate data
followed by unsolicited burst), the initiator must stick with that
decision.

>      10.3.1  Flags and Task Attributes (byte 1)
>
>           The flags for a SCSI Command are:
>
>           bit 0   (F) is set to 1 when no unsolicited SCSI Data-Out PDUs
>                 follow this PDU.  When F=1 for a write and if Expected Data
>                 Transfer Length is larger than the DataSegmentLength, the
>                 target may solicit additional data through R2T.

Take care,

Bill