Re: iscsi: comments to iSCSI rev 6

[julian_satran@il.ibm.com]

Santosh,

This subject was discussed several times. The reason for using the LUN is
to enable iSCSI proxies (or virtualizing devices) to operate as routers in
the host to LUN direction and have them possibly insert the LUN field in
the LUN to host direction.  It addition it enables tag allocation per LUN
(not per target).

Clearly the LUN could be any other routing tag but the LUN is already a
well understood mechanism and will guarantee interoperability.

I wonder if we should not make the LUN a mandatory field for NOP-out in
general and enable "path checking" up to
the LU when the using proxies.

As for the tag name - it would be missleading as we do not require it to
identify uniquely a task.

Julo



Santosh Rao <santoshr@cup.hp.com> on 04-05-2001 03:07:24

Please respond to Santosh Rao <santoshr@cup.hp.com>

To:   Matt Wakeley <matt_wakeley@agilent.com>, Julian
      Satran/Haifa/IBM@IBMIL
cc:   IPS Reflector <ips@ece.cmu.edu>
Subject:  Re: iscsi: comments to iSCSI rev 6




Matt Wakeley wrote:

> > Section 2.12.3: indicate that the LUN is copied from the NOP-IN.  This
is
> > much more clear than "the correct value for the task".
> >
> > +++ and open it up to strange thing like LU5 asking a nop-out to LU7 ?
+++
>
> How will that occur?  The target sent the NOP-IN ping request.  The
target
> includes a LUN.  The only "correct value" that the initiator can return
for
> the LUN in the NOP-OUT ping response is the value the target sent in the
> original request.

Julian,

Re-wording the LUN descriptions in NOP-IN & NOP-OUT to read that
initiators MUST echo the LUN field from a received NOP-IN into a NOP-OUT
is a more clear and un-ambiguous definition than the current text.

That said, I still continue to have reservations about the need for a
LUN field in a non-SCSI PDU. Fibre Channel does not use the LUN field in
its ELS' & BLS'. LUN is a SCSI construct and it must not be used in
non-scsi PDUs.

I'm yet to hear strong reasons why LUN is required in the NOP-IN or
NOP-OUT. The originator of the NOP operation must generate task tags
independent of LUNs for non-SCSI PDUs. Such PDUs have no scsi context.

As a side cosmetic comment, can we re-name "Target Transfer Tag" to
"Target Task Tag" to have symmetry with the use of Initiator Task Tag ?

- Santosh
 - santoshr.vcf