SAM UML and question about command priority and Task manager/device server
Kevin D Butt
kdbutt at us.ibm.com
Tue Jun 10 13:06:18 PDT 2014
Formatted message: <a href="http://www.t10.org/cgi-bin/ac.pl?t=r&f=r1406101_f.htm">HTML-formatted message</a>
Fred,
If your assertion is correct (and I must admit I cannot find anything in
SAM to disprove it), then as SAM is written today, an application client
can send cmd1, cmd2, cmd3, abort(cmd3) and the device server can process
those requests as abort(cmd3), cmd1, cmd2, cmd3 and the application client
has been told cmd3 was aborted and then at a later time will get a STATUS
for cmd3.
On the device, cmd1, cd2, and cdm3 have all been processed and the medium
potentially change by cmd3 with the application client non the wiser.
Is this what you are saying?
Thanks,
Kevin D. Butt
SCSI Architect, Tape Firmware, T10 Standards
Data Protection & Retention
MS 6TYA, 9000 S. Rita Rd., Tucson, AZ 85744
Tel: 520-799-5280
Fax: 520-799-2723 (T/L:321)
Email address: kdbutt at us.ibm.com
http://www-03.ibm.com/servers/storage/
From: "Knight, Frederick" <Frederick.Knight at netapp.com>
To: Kevin D Butt/Tucson/IBM at IBMUS,
Cc: "george.penokie at lsi.com" <george.penokie at lsi.com>
Date: 06/10/2014 12:40 PM
Subject: RE: SAM UML and question about command priority and Task
manager/device server
That sub-clause covers commands also. It asserts the lack of ordering
requirements for everything (commands and TMFs).
Since a command sent before the TMF to abort it could actually arrive at
the device after the TMF arrives, I?m not sure I agree.
The task manager / device server would be trying to abort a command that
the device doesn?t know about yet (because the TMF arrived before the
command arrived). And, by the time the command is received, the TMF could
have already completed.
I don?t see anything in SAM that prevents this. I know that forcing
ordering makes things a lot easier, but I don?t see that SAM does that; in
fact, it seems that is explicitly does NOT require it.
Fred
From: Kevin D Butt [mailto:kdbutt at us.ibm.com]
Sent: Monday, June 09, 2014 6:22 PM
To: Knight, Frederick
Cc: george.penokie at lsi.com; owner-t10 at t10.org; T10 Reflector
Subject: RE: SAM UML and question about command priority and Task
manager/device server
Fred,
This statement talks to the ordering of one task management request
related to another. My ordering comment was a task management request
related to the command at which it is targeted. Therefore, my statement
is that the task manager is required to manage commands and task
management requests in such a manner as to ensure that a task management
request aimed at a command received by the task manager prior to the task
management request not be sent to the device server prior to the command
that it is aborting.
Thanks,
Kevin D. Butt
SCSI Architect, Tape Firmware, T10 Standards
Data Protection & Retention
MS 6TYA, 9000 S. Rita Rd., Tucson, AZ 85744
Tel: 520-799-5280
Fax: 520-799-2723 (T/L:321)
Email address: kdbutt at us.ibm.com
http://www-03.ibm.com/servers/storage/
From: "Knight, Frederick" <Frederick.Knight at netapp.com>
To: Kevin D Butt/Tucson/IBM at IBMUS, T10 Reflector <t10 at t10.org>, "
george.penokie at lsi.com" <george.penokie at lsi.com>,
Date: 06/09/2014 03:15 PM
Subject: RE: SAM UML and question about command priority and Task
manager/device server
Sent by: <owner-t10 at t10.org>
I don?t think your ordering assumptions align with what SAM says (there
are no ordering requirements for TMFs in SAM). It is up to the
application client to do any ordering (if it really wants it). Here is
what SAM already says about this:
4.4.3 Server request/response ordering
?
The order in which task management requests are processed is not specified
by the SCSI architecture model.
The SCSI architecture model does not require in-order delivery of such
requests or processing by the task
manager in the order received. To guarantee the processing order of task
management requests referencing a
specific logical unit, an application client should not have more than one
such task management request pending
to that logical unit.
Fred
From: owner-t10 at t10.org [mailto:owner-t10 at t10.org] On Behalf Of Kevin D
Butt
Sent: Monday, June 09, 2014 5:20 PM
To: T10 Reflector; george.penokie at lsi.com
Subject: SAM UML and question about command priority and Task
manager/device server
In the last SAM conference call, a couple of us were thinking that the
command priority should not only be determined by the device server but
also the task manager.
I was one of those who thought this. I have since repented of that sin.
;-)
I now believe that allowing the task manager to be part of prioritizing
the commands would actually break the model and it should not be allowed.
After reviewing this internally, it was pointed out to me that the task
manager must maintain proper serialization in some aspect if it is going
to be able to properly manage task management functions. Those TM
functions need to be sent after the commands and not before. This infers
that the commands and task management functions must be serialized by the
task manager (in some fashion). If command priority were to be managed by
the task manager, this would either break that model or at least make it
much more complex.
Thanks,
Kevin D. Butt
SCSI Architect, Tape Firmware, T10 Standards
Data Protection & Retention
MS 6TYA, 9000 S. Rita Rd., Tucson, AZ 85744
Tel: 520-799-5280
Fax: 520-799-2723 (T/L:321)
Email address: kdbutt at us.ibm.com
http://www-03.ibm.com/servers/storage/
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