Subject: RE: [Ips] iSCSI: Followup to TMFs/iSCSI Cross Nexus requirement

From: "Pittman, Joseph" <[email-masked]>
Date: Mon, 14 Nov 2005 11:43:23 -0500

Julian,
Thanks very much for your response.
 
> Since timing on different I_T nexii is "unrelated" I guess that the
rule
> about making sure that all preceding statuses have been received
before
> giving the response to the abort/clear task set command that cause the
> "multi-nexi" effect applies only to one nexi the originating (all the
> others are required to some other report form by SAM- TASK ABORTED or
> TASK CLEARED BY ANOTHER INITIATOR).
 
Yes, that is exactly what I am arguing for -- the 'preceding statuses
must be received' ordering requirement should apply ONLY to the issuing
nexus itself.  NOT to the other affected nexuses.

> However the last paragraph of SAM2 - 5.7.3 - require some ordering
(still
> puzling to me) between completing those tasks and entering new tasks
in
> the command set.
 
The ordering requirement in SAM2/5.7.3 is much weaker than the
iSCSI-imposed requirement to which I am objecting:
 
1) The SAM2 requirement is entirely within nexus.  The I_T_L nexus
   handler can cooperate with its transport layer to satisfy the
   SAM2 requirement independently of other I_T_L nexus handlers.
 
2) SAM2/5.7.3 says should, not MUST.

> Since the command set in those cases is a "multi-initiator" command
set
> the meanings by which that sequencing can be achieved are unclear
(provided
> it can be achieved).
> That drove us to suggest ordering by the target.
 
In my opinion, any lack of clarity within the SCSI specs should be
addressed at the SCSI layer, within the SCSI specs themselves.
 
The SCSI protocol places certain requirements on its transport
protocols.  It is within the scope of the iSCSI spec to talk
about how the SCSI requirements are satisfied in iSCSI.
But, in my opinion, it is clearly outside the scope of a transport
protocol to impose additional requirements, like the cross-nexus
requirement to which I am objecting, which impact the SCSI layer.

> I am also not sure that before iSCSI a target supporting different
nexi
> using different transports has been considered - but SAM does not
exclude
> it either.
 
I agree.
But note: I don't think the 'different transports' question is really
the issue here.  This is really just an question of architectural
layering.

--
Joe Pittman
[email-masked]

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---

From: Julian Satran <[email-masked]>
Date: Mon, 14 Nov 2005 20:29:03 +0200

Joseph,

The lingo used by T10 documents in IETF documents is somewhat different.
Should in T10 is MUST in IETF.

More in text.

"Pittman, Joseph" <[email-masked]> wrote on 14-11-2005 

rule
before
(still
in
set
(provided
> addressed at the SCSI layer, within the SCSI specs themselves.

The SCSI text is not unclear. And the cross nexi requirements are a direct 
result of SCSI allowing cross nexi task sets and requiring a certain 
behavior in face of aborts.

The iSCSI text is also not as restrictive as you make it sound.
In the absence of ordering (ordered queue) the composition of the task set 
is entirely at the discretion of the target.
However for every command issued the initiator should receive either a 
good status or a task aborted status and tasks issued after the response 
to abort (that may be indirectly perceived by all initiators) must not be 
aborted.
The iSCSI text says only that the means to achieve this behavior are 
transport dependent and not that the target must wait for all initiators 
acknowledging status before it issues the response to the TM function.

nexi
exclude