Subject: iSCSI - change proposal LUN field definition on every PDU

From: "Julian Satran" <[email-masked]>
Date: Mon, 12 Nov 2001 14:30:38 +0200

Dear colleagues,

A colleague interested in instrumentation approached me with a question 
about stateless logging of specific LU activity.
With the current iSCSI PDU formats this is not possible.
We have consistently avoided having fields that are redundant and will 
need consistency checking.
However I think we should consider including the LU field in all PDUs that 
are referencing a specific LU to simplify this type of instrumentation (as 
we did with the direction bit in the op-code).

As I am already in "count-down" mode for version 09 I would appreciate 
your comments ASAP.

Julo

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From: Paul Koning <[email-masked]>
Date: Mon, 12 Nov 2001 12:02:28 -0500

> we did with the direction bit in the op-code).

NO.

I can see no good reason to add work to an implementation fastpath for
this.  It slightly simplifies instrumentation, but instrumentation is
certainly possible without it.  That is sufficient.

       paul

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From: "Ken Sandars" <[email-masked]>
Date: Mon, 12 Nov 2001 18:19:22 -0000

Hi Julo,

Anything which helps get diagnostic and measurement equipment out
is a GOOD thing, especially when there is a kick back to those who
speak up in support ;-)

Are the only changes to the SCSI Response, the Task Management
Response and the Data-In PDUs?

Cheers,
Ken
[email-masked]
Eurologic Systems
+44 117 930 9616

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From: Santosh Rao <[email-masked]>
Date: Mon, 12 Nov 2001 10:55:01 -0800

Julian,

Can you explain further the extent of PDUs that are intended to be
affected by this change ? Also, can you clarify why it is not a problem
for other SCSI transport protocols like FC where the LUN field is not
included in every FC IU ?

IMO, the LUN knowledge is best kept out of the SCSI transport as far as
possible. All LUN level logging/tracing belongs to the SCSI ULP, which
is given a LUN context on each call made to it from the LLP.

At the SCSI LLP layer, tracing/logging as well as state information
should be at the I-T nexus level (session).

I don't (yet) see a sufficient justification for this change. Perhaps,
more information on the motivation for this request may change that.

- Santosh

-- 
##################################
Santosh Rao
Software Design Engineer,
HP-UX iSCSI Driver Team,
Hewlett Packard, Cupertino.
email : [email-masked]
Phone : 408-447-3751
##################################

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From: "Mallikarjun C." <[email-masked]>
Date: Mon, 12 Nov 2001 11:44:21 -0800

> possible.

I agree.  

I also agree with Paul Koning about the perf path implications for
software implementations.

In addition, more significantly, I am concerned about the consistency 
checking aspects of this change.  Apart from the performance costs 
incurred because of checking, what if the LUN doesn't match the 
active ITT?  In general, more errors (and possibly Reject reasons).

Lastly, it appears to me that the general philosophy of relying only
on ITT for instantiated tasks is not applied here (given that ITT
is unique per session across all LUNs).

To summarize, IMHO, these disadvantages outweigh the benefit of 
stateless logging of LUN traffic.
-- 
Mallikarjun 

Mallikarjun Chadalapaka
Networked Storage Architecture
Network Storage Solutions Organization
MS 5668	Hewlett-Packard, Roseville.
[email-masked]