RE: Response Fence Flag

Mallikarjun,

OK, so I would like us to first cover Topic A (your case 1).

As I understand it you are trying to make TMC and ACA operate correctly
on a MC/S Session.  

 

And, if I understand your Slide 5, et.al. correctly then the iSCSI code
can ASSUME a Fence has been issued for all TM and ACA operations and
react as you have specified.  In that specific case there is no need for
Fence parameter in the Target SCSI to iSCSI interaction (at least at
this time).

 

So if that is the case, then for all current operations we are covered
without additional Target SCSI parameters.  Is that correct?

 

Now when you use the words Third Party Session, I believe that could
mean Session that are iSCSI or Non iSCSI (e.g. Fibre Channel), I also
think it could include iSCSI Sessions on other portal groups connected
to the same Target. 

 

The thing that is concerning me is that some of the words which are
included in the document do not factor in the fact that any specific
iSCSI Target portal group may not have a clue about what is happening at
another iSCSI Target portal group, or at a Fibre Channel portal that may
also be attached to the same Target/LUN.

 

The way I read your document, I thought that it implied that the iSCSI
Transport would know about things that are happening on other Portal
Groups that may be iSCSI or some other Transport technology.

 

For instance in section 4.1.3.a (under the Target iSCSI Layer) you state
"...SHOULD NOT wait for new commands on third-party affected sessions -
only the instantiated tasks have to be considered for the purpose of
determining the affected tasks."  Other than the fact that it does not
matter what the other Session do, since you ignore it, the thought
pattern is that you will know that you are ignoring it.
 
Also in section 4.1.3 d (under the Target iSCSI layer) you state
"...MUST generate an Asynchronous Message PDU with AsyncEvent=5 (section
8.1) on: 
          i) each connection of each third-party session that at 
            least one affected task is allegiant to, and 
          ii) each connection except the non-issuing connection of the 
            issuing session that has at least one allegiant affected 
            task. "
 
I think that implies that one iSCSI portal group has knowledge of what
is happening in other portal groups, and that extends to other
Technology attachments such as Fibre Channel.
 
If you are stating that it is up to the target SCSI layer to issue the
"Fence parameter" appropriately such that the effect is what you stated
in 4.1.3 (under the Target iSCSI Layer) then I might feel that I am
coming closer to understanding your point.
 
Otherwise, I just do not see how that is practical since even the iSCSI
target portal groups may be implemented in separate iSCSI Offload
Adapters.  And I really do not know how they will know what is happening
on the Fibre Channel connections. 

 

When I combine the above thought with the statements that were made by
Robert Snively, which in effect states that all the actions and
responses arrivals are not predictable (at least across different
Sessions), that seems to me to mean that the appearance of UAs, caused
by another Session, may occur at any time with relation to what is going
on at any other Session.  Therefore, I can not yet grasp the need for
ordering Asynchronous Messages among the MC/S connections.  I am trying
to see what the initiator surprise will be, and why that will cause a
problem, if the Asynchronous Messages occur in some undefined order.
However, at this time I am left with an unease that not only are some of
the above document statements not implementable, I am wondering it they
are even important.

 

Hopefully, you can understand my dilemma on understanding what you are
proposing, and can explain what I am missing.

 

.

.

.

John L Hufferd

Sr. Executive Director of Technology

Brocade Communications Systems, Inc

[email protected]

Office Phone: (408) 333-5244; eFAX: (408) 904-4688

Alt Office Phone: (408) 997-6136; Cell: (408) 627-9606

 

________________________________

From: Mallikarjun C. [mailto:[email protected]] 
Sent: Friday, January 05, 2007 2:45 PM
To: IPS
Subject: Fw: [Ips] Response Fence Flag

 

Trying again after bouncing (>50KB), tail is now clipped....

----- Forwarded Message ----
From: Mallikarjun C. <[email protected]>
To: [email protected]
Sent: Friday, January 5, 2007 2:40:56 PM
Subject: Re: [Ips] Response Fence Flag

Hi John,

 

As you correctly point out, there are two distinct but related topics
here.

 

(1) proper response ordering across participating connections in a
multi-connection session, for a handful of task/TMF responses

(2) proper way to terminate and signal tasks when actions on one session
can impact multiple initiators

 

(1) is all about response fence, it is covered separately in section 3.3
of IG draft.  That's what this email thread started off with.

 

(2) covers cases that IG had called as as "multi-task abort" cases that
typically have a shared task set across sessions, or are the result of a
Logical Unit Reset TMF.  Section 4.1 of IG adresses (2).

 

So how are (1) and (2) related?

 

- Some cases covered under (2) overlap with (1), but some cases in (2)
are for single connection sessions.  E.g. LU Reset on a single
connection session impacting several 3rd party sessions

 

- Some cases under (1) overlap with (2), but some cases in (1) have
nothing to do with other sessions.  E.g. establishment of ACA on a
non-shared task set

 

- Section 4.1 (i.e. text for (2)) uses response fence (i.e. text for
(1)) whenever multi-connection sessions are involved in multi-task abort
situations.

 

I hope that clarifies it.  Feel free to ask if that is not clear.  The
net is that the response fence is the underpinning notion to describe
the correct iSCSI behavior in a few cases and some of those cases are
about task terminations across third-party sessions.

 

Mallikarjun

 



 

----- Original Message ----
From: John Hufferd <[email protected]>
To: Mallikarjun C. <[email protected]>; [email protected]
Sent: Friday, January 5, 2007 1:01:06 PM
Subject: RE: [Ips] Response Fence Flag

Mallikarjun,

I must admit, that I have been a bit confused with the direction of the
conversation here.

 

Therefore, I went back and reviewed the charts from Dallas .  And as I
remembered, the initial focus was to address the issue of Multiple
Connections per Session (MC/S) (as stated on chart 4 - "Non-issue for
single-connection iSCSI sessions").  So I think I have missed the step
where we have morphed the discussion into one dealing with multiple
sessions.  (I am not sure how that happened, or if I miss-read the
charts from Dallas , or have not followed the discussion adequately.)

 

If we are attempting to define two different issues, one with MC/S and
one with Multiple Session from different Initiators, I think it would be
useful to break down the conversation into Topic A - MC/S and Topic B
Multiple Sessions.  It is possible that one solution will addresses
both, but I for one think I am hearing arguments that might be
appropriate for Topic B, while I am thinking about its applicability to
Topic A.

 

Perhaps, you could address the issue as either being all about MC/S or
explicitly state that it is intended to affect Multiple Sessions also,
and then address the issues and solution for each separately.  For
example, I believe Robert was addressing the issue from a view of
Multiple Sessions and if we only intended to address MC/S then I expect
the response might be somewhat different.

 

Anyway, if you could clear-up some of this, I think it would be useful
(at least to me).

 

.

.

.

John L Hufferd

Sr. Executive Director of Technology

Brocade Communications Systems, Inc

[email protected]

Office Phone: (408) 333-5244; eFAX: (408) 904-4688

Alt Office Phone: (408) 997-6136; Cell: (408) 627-9606

 

________________________________

From: Mallikarjun C. [mailto:[email protected]] 
Sent: Friday, January 05, 2007 10:08 AM
To: [email protected]
Subject: Re: [Ips] Response Fence Flag

 

Not really.  Current draft text is intentionally written to not have any
dependencies on T10 dynamics.  The point is that iSCSI needs such a
notion for succinctly describing the proper iSCSI protocol actions in a
few places - ACA, TMF, Persistent reserve/Abort to name a few.  We
certainly hope it will be approved by T10 and be a part of SAM-4 soon,
but that isn't required per se for describing what iSCSI needs for its
correct behavior.

 

IPS WG has adopted what it needs in the past - staying ahead of T10
review/approval cycle if necessary.  I_T nexus loss notification, iSCSI
target/port naming, clearing effects are a few I recall.

 

Mallikarjun



 

----- Original Message ----
From: Eddy Quicksall <[email protected]>
To: Robert Snively <[email protected]>; "Elliott, Robert (Server
Storage)" <[email protected]>; [email protected]
Sent: Friday, January 5, 2007 8:58:47 AM
Subject: Re: [Ips] Response Fence Flag

>From an earlier email I think that Response Fence is only a proposal in
T10 (http://www.t10.org:80/doc06.htm <http://www.t10.org/doc06.htm> ).
If so shouldn't iSCSI wait a bit until this has been ratified?

 

Eddy


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