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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
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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