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

["Julian Satran" <Julian_Satran@il.ibm.com>]

Santosh,

We are talking about instrumentation that could work based only on what is 
on-the-wire.
For an instrument (software I assume) that sits between SCSI and iSCSI 
this is obviously not an issue.
It is not a major issue for an instrument on the wire (it must maintain 
some state anyhow) but telling something about traffic based on the field 
might simplify it.  We can also make this field "not mandatory to test by 
receiver" to avoid having the receiver pay a penalty.

As for the PDUs - SCSI Response, Data-Out & In and Task Mangement 
request/response.

I am not sure what other uses or side-effects this change may have.

Julo




Santosh Rao <santoshr@cup.hp.com>
Sent by: santoshr@cup.hp.com
12-11-01 20:55
Please respond to Santosh Rao

 
        To:     Julian Satran/Haifa/IBM@IBMIL
        cc:     ips@ece.cmu.edu
        Subject:        Re: iSCSI - change proposal LUN field definition on every PDU

 

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



Julian Satran wrote:
> 
> 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

-- 
##################################
Santosh Rao
Software Design Engineer,
HP-UX iSCSI Driver Team,
Hewlett Packard, Cupertino.
email : santoshr@cup.hp.com
Phone : 408-447-3751
##################################