SAM UML and question about command priority and Task manager/device server

Knight, Frederick Frederick.Knight at netapp.com
Mon Jun 9 15:08:22 PDT 2014


Formatted message: <a href="http://www.t10.org/cgi-bin/ac.pl?t=r&f=r1406095_f.htm">HTML-formatted message</a>

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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