FCP-4: I_T Nexus Reset

Knight, Frederick Frederick.Knight at netapp.com
Fri Oct 29 11:55:23 PDT 2010

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There are several references to I_T Nexus loss (clauses 3.1.24, 3.1.25,
4.11, 6.4).  It sounds like you agree with my suggested resolution that
Table 4 - task management functions, SAM-4 to FCP-4
Add a row that says:
I_T_NEXUS_RESET 		       LOGO ELS (see FC-LS-2)
This does not change its optional-ness.  If it is supported, this is how
you do it (via LOGO).  This isn't much different than saying QUERY TASK
translates to REC ELS.
Application clients can't issue a LOGO.  They can issue SAM functions
(such as I_T_NEXUS_RESET).
The reason I brought this up, is because of the same reason we've
introduced a new iSCSI draft to update iSCSI to SAM-4/5 - and that is -
many host vendors refused to use some new SCSI features because it
required them to become transport aware at the class driver layer.  When
hosts must know the transport to be able to determine what parts of the
SCSI protocol work and what parts don't, they would simply prefer to
never use that function anywhere, because they never know whether it
will work or not.
That is the driving force to add it - to again make it possible to write
a transport agnostic class driver.
		Fred Knight
From: Bob.Nixon at Emulex.Com [mailto:Bob.Nixon at Emulex.Com] 
Sent: Wednesday, October 27, 2010 5:11 PM
To: dpeterso at brocade.com; t10 at t10.org
Subject: RE: FCP-4: I_T Nexus Reset
Hi, Dave, I_T_NEXUS_RESET was invented to provide a function similar to
Fibre Channel LOGO for transports that did not have the concept of
login/logout. Out of respect for established transports that had
login/logout, and for which the equivalent TMF was irrelevant,
I_T_NEXUS_LOSS was specified as optional to support.
I believe there is still no reason for FCP-x to support I_T_NEXUS_RESET;
however, FCP should make that a little more obvious.
I'd suggest adding a row to table 4 (Task management functions, SAM-4 to
I_T_NEXUS_RESET...Not Supported
The "Not Supported" statement should reference a table footnote
A Logical Unit that receives a "Report Supported Task Management
Functions" command (see SPC-4) and is aware that the command has been
received via FCP should set the ITNRS bit to zero in the reply,
indicating the I_T NEXUS RESET task management function is not
-	   bob
From: owner-t10 at t10.org [mailto:owner-t10 at t10.org] On Behalf Of David
Sent: Wednesday, October 27, 2010 11:54 AM
To: t10 at t10.org
Subject: FCP-4: I_T Nexus Reset
FCP-4 letter ballot NetApp-001 states:
"This table maps SAM-4 functions to FCP-4 functions - but the SAM I_T
NEXUS RESET function is missing (table 7 seems to indicate that LOGO ELS
has the appropriate clearing effect)."
Other than this letter ballot comment I have received no requests to
provide I_T NEXUS RESET support in FCP-4.
Please respond with your preference to include I_T NEXUS RESET in FCP-4
or not, along with your reasoning.

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