RE: iSCSI: Implicit Termination of Tasks

["Elliott, Robert (Server Storage)" <Elliott@hp.com>]

A few comments on this thread:

* Autosense protocols simply do not have CA.  At the T10 CAP meeting
this week, Ralph Weber is proposing removing all references to CA from
SAM-3 (see 03-002r2 on http://www.t10.org).  As soon as a command
completes, it is assumed that the status and sense data will be returned
together.  If they can't be delivered, it doesn't matter.

* the clearing effects table in FCP-2 was removed because it had several
incorrect entries and was missing quite a few additional SCSI items that
are also affected by logouts.  T10 proposals 02-143r3 and 02-232r2 have
the details and include large tables listing all the considered SCSI
effects.  These proposals have been incorporated into the latest SAM-3,
SPC-3, SBC-2, and SSC-2 standards.

* Most protocols don't detail how their hypothetical SCSI layer confirms
the abort of tasks to the protocol layer by specifying a CHECK
CONDITION, much less one with a specific sense key and additional sense
code.  This level of detail is internal only and seems irrelevent to the
iSCSI wire protocol. Specifying a "unit attention" sense key could cause
particular confusion, since unit attentions are supposed to be cleared
once reported.  

On the iSCSI wire, the goal is to generate a unit attention with an
additional sense code whose ASC field is 29h (e.g. I_T NEXUS LOSS, POWER
ON OCCURRED, etc.) on the next command.

To minimize changes to iSCSI at this point, I recommend changing
the wording like this (changed text noted between _ characters)
so only status is mentioned and it is only mentioned as an example:

If the tasks terminated in the above cases a), b, c) and d)are SCSI
tasks, they must be internally terminated _with CHECK CONDITION
status with a sense key of unit attention and ASC/ASCQ values of
0x6E/0x00 (COMMAND TO LOGICAL UNIT FAILED)_. This status is only
meaningful for appropriately handling the internal SCSI state and
SCSI side effects with respect to ordering (e.g., queued commands
and ACA) because this status is never communicated back as a
terminating status to the initiator.

To:
If the tasks terminated in the above cases a), b, c) and d) are SCSI
tasks, they must be internally terminated _as if with CHECK CONDITION
status_.  This status is only
meaningful for appropriately handling the internal SCSI state and
SCSI side effects with respect to ordering (e.g., queued commands
and ACA) because this status is never communicated back as a
terminating status to the initiator.

---
Rob Elliott, HP Industry Standard Server Storage
elliott@hp.com 

-----Original Message-----
From: Eddy Quicksall [mailto:eddy_quicksall@ivivity.com] 
Sent: Thursday, January 09, 2003 2:39 PM
To: dcuddihy@attotech.com; ips@ece.cmu.edu
Subject: RE: iSCSI: Implicit Termination of Tasks


The way I figured it would work is that the UA would get set and would
get reported when the next command arrives.

Consider this:

connection 0 and 1 are all quite
connection 0 has a command x on the wire
connection 0 is lost
the UA is set
command y comes in connection 1
command y gets the UA or ACA Active

That way the upper layer at the initiator can figure out how to recover.

Is this not the idea?

Eddy

-----Original Message-----
From: dcuddihy@attotech.com [mailto:dcuddihy@attotech.com]
Sent: Thursday, January 09, 2003 3:05 PM
To: ips@ece.cmu.edu
Subject: RE: iSCSI: Implicit Termination of Tasks


David,

Regarding Autosense clearing the CA:

The problem that I have with this is that the CA should get cleared when
the sense data is reported, not when the sense data is generated.  In
this case, the autosense cannot be reported (the port is logged out), so
the CA may not be cleared. It doesn't seem to me that generating a sense
data response, even for an interface in which autosense is mandatory,
implicitly clears a CA.

By the way, there was a question of Request Sense commands enqueued when
a termination occurs .. my understanding is that the sense data need not
be saved for a subsequent request sense command if it has been reported
via autosense, so the request sense returns NO_SENSE.

Regarding FCP handling of port logout and ACA:

For us, ACA is a non-issue-- we don't support it, but it should be
cleared only for the initiator which generated the log event.  (ACA
support seems to be a point of contention among SCSI implementers... I
know it's in all the specs, but I have yet to see it implemented.)

Rev 7A of FCP-2 has a nice chart of how task managment is affected via
the various log events.  I'm not why it was removed in rev 8, but "FCP-2
Rev 7A (1/1/2001)" Table 4 might help.

regards,

david




David J Cuddihy
Principal Engineer
ATTO Technology, Inc.
http://www.attotech.com/fcbridge.html
dcuddihy@attotech.com

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David,

> Forgive me for being confused, but what is the reason for the Check 
> Condition being issued?

Good question ...

> Say a target implements a blocking CA, (TST 0 Qerr 0) which would
disallow
> other initiator's tasks from running until the check condition could 
> be reported, or another command from the CA'd initiator completes with

> good status.  An internal, non- reported check-condition would cause 
> all other initiators' tasks to be blocked until  someone times out and

> issues a lun reset to the device, or a command from the first 
> initiator completed (not likely, since that initiator logged out and
all its tasks have been
> terminated ).    All this caused by bad behavior on behalf of one
> initiator.

That shouldn't happen.  iSCSI REQUIRES use of Autosense, which will
immediately clear the CA by generating a response to report the sense.
That response gets bit-bucketed as undeliverable for the implicit
termination scenarios in Section 6.5, but its generation clears the CA.
Not the most obvious thing to do/explain, though ...

> Implicit termination is handled in FCP without the check condition 
> being issued... all the tasks from the 'logged out' initiator are 
> terminated, reservations cleared, etc.  and a UA is generated for that

> initiator. Every other initiator goes along with no problem, including

> those sharing the lun with the initiator who abruptly logged out.  
> Seems to work.

That looks like a cleaner way to accomplish this and avoids some of the
confusion over what ASC/ASCQ values to use.  Does FCP also avoid ACA in
this circumstance (assuming that NACA is set to use ACA), and if so, can
you suggest some specific text for iSCSI?

Thanks,
--David
----------------------------------------------------
David L. Black, Senior Technologist
EMC Corporation, 176 South St., Hopkinton, MA  01748
+1 (508) 293-7953 **NEW**     FAX: +1 (508) 293-7786
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