Subject: Re: iSCSI:Clear Task Set

From: "Julian Satran" <[email-masked]>
Date: Sat, 24 Nov 2001 09:06:29 +0200

John,

That looks more like in  T10 territory.
T10 defines differently Abort Task Set and Clear Task Set.
We could either:

decide not to implement clear task set (T10 allows that but "per target" 
not "per transport")
enable clear task set - in which case we have to say something about the 
relative order of the task management request with regard to the  task 
comming from other initiators - and that is what I attempted to say in 9.4 

Julo

John Hufferd/San Jose/IBM@IBMUS
Sent by: [email-masked]
23-11-01 23:30

        To:     Julian Satran/Haifa/IBM@IBMIL
        cc:     [email-masked]
        Subject:        Re: iSCSI:Clear Task Set

Julian, and list,
The question now becomes, if we have all that carefully thought out
processing that is defined in 9.4 in how to handle the other 
Tasks/Commands
that are "In Flight", and not yet given to SCSI, how does that apply to 
the
other Sessions with other initiators?

That is, at the iSCSI Target layer we do not have the LU Number to LU
mapping on any Session with any Initiator, so how do we cause the careful
processing, which is defined in 9.4, to occur on the other sessions that
may have and association to the subject LU? Especially since all we know 
is
a LU Number on the Clearing Session.

Perhaps we do not care about the 9.4 processing on the other Session and
Other Initiators and just let SCSI layer do its thing, and at the iSCSI
layer we pay no attention to the other Sessions.  Do you think this is
correct?

.
.
.
John L. Hufferd
Senior Technical Staff Member (STSM)
IBM/SSG San Jose Ca
Main Office (408) 256-0403, Tie: 276-0403,  eFax: (408) 904-4688
Home Office (408) 997-6136, Cell: (408) 499-9702
Internet address: [email-masked]

Julian Satran/Haifa/IBM@[email-masked] on 11/23/2001 07:56:36 AM

Sent by:  [email-masked]

To:   [email-masked]
cc:
Subject:  Re: iSCSI:Clear Task Set

John,

The LUN is just a mistake there - in all three instances it should be LU.
The definitions are in accordance with SAM . There are two task management
modes - tasks sets-per-initiator at each LU or common for all initiators.
The mode is a SCSI issue controlled by a field in the Control-Mode page.
Clear task set MAY clear all the tasks in the task set - even if common to
all initiators if that is the way the task set is managed. That is also
the difference between clear-task-set and abort task set.

Julo

John Hufferd@IBMUS
23-11-01 11:29

        To:     Julian Satran/Haifa/IBM@IBMIL@IBMDE
        cc:     [email-masked]
        From:   John Hufferd/San Jose/IBM@IBMUS
        Subject:        iSCSI:Clear Task Set

Julian, and List  (using v 0.9)
In point 9.4, just before 9.5  the Table entry associated with Clear Task
Set applies to:

"All tasks associated with the specified LUN and initiator. For all other
initiators all tasks at LUN with no regard to order."

Perhaps we mean LU here, but I know that the iSCSI layer does not have
information about LU, only about the LU Number (LUN) in the command.  We
can not tell, at the iSCSI layer, if the  LU represented  by a LUN on
Session 1, has any relationship to any LUN on any other session.

This is because each initiator may have their own numbering for LUs.
Therefore, do we just pass the Clear Task Set to the SCSI layer and hope
for the best, or does the iSCSI layer also suppose to apply the Clear Task
Set to all the sessions that it has coming into the iSCSI (SCSI) Target
Port?  If the latter, again how will that work when the iSCSI layer has no
idea what LU an Initiator's LUN will map to?
.
.
.
John L. Hufferd
Senior Technical Staff Member (STSM)
IBM/SSG San Jose Ca
Main Office (408) 256-0403, Tie: 276-0403,  eFax: (408) 904-4688
Home Office (408) 997-6136, Cell: (408) 499-9702
Internet address: [email-masked]

---

From: "Mallikarjun C." <[email-masked]>
Date: Fri, 30 Nov 2001 16:28:17 -0800

Julian,

I tend to agree with John on this one. 

Passing the 'clear task set' onto target SCSI layer once
the current session is dealt with is the right choice.  That
avoids iSCSI having to say anything on the relative order 
across sessions, and also addresses the issue John raised -
that of differing LUN mappings for the same LU.

At a minimum, the second sentence in the current wording  

"All tasks associated with the specified LUN and initiator. 
 For all other initiators all tasks at LUN with no regard 
 to order."

should be dropped since it implies that 'clear task set' affects 
all other initiators.  In fact, this determination can not be made 
until the TST bit is checked in the SCSI control mode page - which 
is completely in the SCSI realm.  That of course requires the task 
management function to be propagated up.

Regards.
-- 
Mallikarjun 

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