Death to I_T_L_Q nexus

Kevin D Butt kdbutt at
Wed Jun 11 11:22:36 PDT 2014

Formatted message: <a href="">HTML-formatted message</a>

I have no objections with the concept of this direction. I was initially 
concerned with the terminology used since FCP-4 also used the term. 
However, upon further review this seems to fall right into place.
FCP-4 Terms:
Command Identifier = 3.1.7 command identifier: The information that 
uniquely identifies a command. See Annex A and SAM-5.  This is synonymous 
with OX_ID (Note that If retransmission is enabled, the task retry 
identifier is also used to construct the command identifier.) 
I do have a concern with using "I_T_L nexus plus command identifier" 
throughout all the standards.  I would prefer we come up with a term to 
describe this.	Perhaps something like "Fully qualified command 
identifier".  I know that doesn't really save words or letters when typing 
it, but it does better convey, I think, the concept for which it is used.
Annex terminology mapping seems to have inconsistencies in it.
For SAM-3 command identifier = task tag
For SAM-4 command identifier = I_T_L_Q nexus
I think, perhaps for SAM-4 mapping it should be "I_T_L nexus plus command 
identifier = I_T_L_Q nexus"
Also, there is a typo of "poert" instead of "port" in in the SCSI 
Initiator Port box
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 
From:	George Penokie <george.penokie at>
To:	T10 Reflector <t10 at>, 
Date:	06/11/2014 08:35 AM
Subject:	Death to I_T_L_Q nexus
Sent by:	<owner-t10 at>
If don't reached SAM overload yet this proposal should push you over the 
edge. Here is the overview:
There has been a long standing problem with the I_T_L_Q nexus as it 
combines routing information with a command identifier. The routing part 
is the I, the T, and the L. The command identifier is the Q. In addition 
the nexus really does not have a satisfactory home in the SAM-5 UML 
This proposal solves the UML issue by adding a Management Application 
Client class that is a ?kind of? Application Client class. The new 
Management Application Client class has I_T Nexus Identifier attributes 
and I_T_L Nexus Identifier attributes. The Management Application Client 
class is the class that goes out and finds all the nexuses in the SCSI 
domain. The method used for the Management Client class to do this is 
protocol specific. For example in SAS the discovery is defined in the SPL 
This also separates Q from nexus and replaces that with a standard alone 
attribute called a Command Identifier attribute. The effect of this is 
that all the I_T_L_Q nexus terms will be replaced with either Command 
Identifier or I_T_L nexus and command identifier. This causes extensive 
changes to several standards but has the largest effect on SPL, then SAM, 
then SPC, and finally SBC. To prevent issues with existing published 
standards the term I_T_L_Q nexus will have to remain but it will be 
defined as being synonymous with I_T_L nexus plus command identifier.
Your request to upload a file or files to the T10 site has been accepted.
Your PDF file will be posted at:
Bye for now, 
George Penokie 
Avago Technologies
3033 41 St NW
Rochester , MN 55901 
george.penokie at

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