RE: bridging issues -- Converging FCP-2 and iSCSI control structures

[meth@il.ibm.com]

Charles,
The "Additional Data" field in the SCSI Command PDU may be used to send
either "immediate data," or  a CDB that is longer than 16 bytes, or both.
To determine whether the "Additional Data" is "immediate data" or part of a
long CDB, the flags (Byte #1, bits 6-7) must be examined.  The most
expected case is that the CDB fits into the allocated 16 byte space, so
only "immediate data" would be in the "Additional Data" field; in this case
the flags (bits 6-7) are 00b. The current specification is not very neat
with regard to this point, but using extra bytes to separate the "immediate
data" length from the extra CDB length would have necessitated expanding
the iSCSI header even more.

How do others think we should clean up this part of the iSCSI header?

The use of "immediate data" is for the case when the data for a command is
small, in which case the entire data may be sent together with the SCSI
Command PDU as "immediate data," thus avoiding the need to send a separate
SCSI Data PDU.

- Kalman



Charles Monia <cmonia@NishanSystems.com> on 19/09/2000 03:09:20

Please respond to Charles Monia <cmonia@NishanSystems.com>

To:   Julian Satran/Haifa/IBM@IBMIL, ips@ece.cmu.edu
cc:    (bcc: Kalman Meth/Haifa/IBM)
Subject:  RE: bridging issues -- Converging FCP-2 and iSCSI control struct
      ures





<... deleted ...>

Julo wrote:
> There is some misunderstanding about the CDB length - the
> iSCSI is pretty
> liberal only that it use a tricky coding of the length field
> (not something
> we would necessarily want to keep in).
>

Charles wrote:
I may well have misunderstood something here.  After reading the iSCSI
spec,
I was not clear as to what the extra data field in the iSCSI command PDU
was
to be used for.  It was my surmise that you may have intended this for CDBs
in excess of 16 bytes -- although, I didn't glean that from the wording in
the spec.

<... deleted ..>

Regards,
Charles