FCP-4: I_T Nexus Reset

Bob.Nixon at Emulex.Com Bob.Nixon at Emulex.Com
Tue Nov 2 10:56:29 PDT 2010


Formatted message: <a href="http://www.t10.org/cgi-bin/ac.pl?t=r&f=r1011020_f.htm">HTML-formatted message</a>

At least a couple things bother me about this:
First, FC is, at least in theory, a multiprotocol channel. If a SCSI
application did an I_T_NEXUS_RESET, and it were mapped to LOGO, all
concurrent applications between the pair of Nx_Ports (e.g., a management ap)
would be blown away.
Second, if a SCSI application on a SAS transport sends an I_T_NEXUS_RESET,
I'm guessing it can then continue to send SAS commands; and further, it will
get any check conditions caused by the I_T_NEXUS_RESET. If the same SCSI
application requests I_T_NEXUS_RESET on an FCP transport, causing an FC
N_Port LOGO, subsequent commands can not be sent until a new LOGIN and PRLI
are completed as well; and I'm not certain that the new login will reliably
be interpreted as a continuation of the activity of the  original I_T nexus;
in which case, the check conditions may not be forthcoming.
-	   bob
From: Knight, Frederick [mailto:Frederick.Knight at netapp.com]
Sent: Friday, October 29, 2010 11:55 AM
To: Nixon, Bob; dpeterso at brocade.com; t10 at t10.org
Subject: RE: FCP-4: I_T Nexus Reset
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
I_T_NEXUS_RESET = LOGO:
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
FCP-4):
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 supported.
-	   bob
From: owner-t10 at t10.org [mailto:owner-t10 at t10.org] On Behalf Of David
Peterson
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.
Thanks...Dave



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