SAM UML and question about command priority and Task manager/device server
Kevin D Butt
kdbutt at us.ibm.com
Mon Jun 9 15:22:18 PDT 2014
Formatted message: <a href="http://www.t10.org/cgi-bin/ac.pl?t=r&f=r1406096_f.htm">HTML-formatted message</a>
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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