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RE: iSCSI: Implicit Termination of Tasks
Yes
and this is where I've been coming from since I started this thread. 6.5 should
be changed as Bob pointed out below. I can't tell from your response "This is
perfectly reasonable" if you are agreeing that Bob's suggestion is reasonable or
if the current wording is reasonable.
Please
clear that up.
Eddy
Eddy,
Setting the UA is a purely SCSI matter
and so is the code used. There is no iSCSI state surviving and we assume that
the isCSI initiator
produces some
termination code for the SCSI initiator. It is not clear to me than anything
besides "ACA active" code is needed.
If the target messes with command from other initiators (single
queue-per-target) those should be ready to accept the consequences of a
common queue.
UA is used (IMHO) mostly
in cases of reset - that kill commands in other queues even when the operation
is queue-per-initiator.
Julo
| "Eddy Quicksall"
<Eddy_Quicksall@iVivity.com>
14/01/03 16:39
|
Please respond
to
<Eddy_Quicksall@iVivity.com> |
|
|
To
| Julian
Satran/Haifa/IBM@IBMIL
|
|
cc
| <Black_David@emc.com>, <dcuddihy@attotech.com>,
<ips@ece.cmu.edu>, "Elliott, Robert \(Server Storage\)"
<Elliott@hp.com>
|
|
Subject
| RE: iSCSI: Implicit
Termination of Tasks |
|
>>nothing specific has to survive for ACA
For ACA,
doesn't the next command get the UA then the additional commands get ACA
Active until ACA is cleared (all assuming NACA, the ACA attribute and QErr are
being used appropriately)?
So, doesn't the UA have to survive?
Eddy
-----Original
Message-----
From: Julian Satran
[mailto:Julian_Satran@il.ibm.com]
Sent: Tuesday, January 14, 2003
3:50 AM
To: Elliott, Robert (Server Storage)
Cc:
Black_David@emc.com; dcuddihy@attotech.com; Eddy Quicksall;
ips@ece.cmu.edu
Subject: RE: iSCSI: Implicit Termination of
Tasks
Rob,
This is perfectly reasonable.
The clearing effects will wipe-out anyhow whatever was specific to the
code for session termination
and nothing specific has to survive for ACA.
Regards,
Julo
| "Elliott, Robert (Server
Storage)" <Elliott@hp.com>
14/01/03 09:59
|
|
To
| "Eddy
Quicksall" <eddy_quicksall@ivivity.com>,
<dcuddihy@attotech.com>, <ips@ece.cmu.edu>, Julian
Satran/Haifa/IBM@IBMIL, <Black_David@emc.com>
|
|
cc
|
|
|
Subject
| RE: iSCSI: Implicit
Termination of Tasks |
|
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
------------------------------------------------------------------------
----
---------------------
------------------------------------------------------------------------
----
---------------------
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
black_david@emc.com Mobile: +1 (978)
394-7754
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