FC-TAPE Command Reference Numbers

[Baldwin, Dave]

* From the T10 (formerly SCSI) Reflector (t10 at symbios.com), posted by:
* "Baldwin, Dave" <Dave.Baldwin at emulex.com>
*
Bob,

PLEASE put the PRLI CRNS bit back in to the FCP-2 document. We have =
discussed this issue previously in the FC-TAPE working group, and the =
decision was to provide this feature.

Some companies have control over all pieces of the operating systems =
they have to deal with, so your proposal would make sense in these =
environments.

Other companies, like mine, need to provide HBA device drivers that run =
on several different operating systems. We do not have a lot of =
influence over operating system vendors, and can't get them to put the =
necessary changes in required by your implementation. Some still can't =
support more than 16 targets per adapter board, or more than 8 LUNs per =
target, which for us would be a higher priority than implementing the =
ECRN functionality. We don't have several years before we need this =
behavior, we need it now.

HBA drivers are not supposed to be doing MODE SENSE/SELECT commands, and =
doing so would be very distasteful. Using the CRNS bit to determine =
whether the HBA driver provides a CRN in the FCP_CMD is a very simple =
and very useful mechanism. Please reconsider your decision.

Best regards,
Dave Baldwin
Emulex Network Systems

----------
From: 	Bob Snively
Sent: 	Thursday, October 29, 1998 10:44 AM
To: 	fc at nsco.network.com; t10 at symbios.com
Subject: 	FC-TAPE Command Reference Numbers


While working on the FCP-2 document, I thought long and carefully about
how we use CRN.  I have made the following adjustments in the first =
revision
of FCP-2.  I hope everybody likes them.

1)  Naming the function

I have arbitrarily named the function provided by CRN as "precise =
ordering".

2)  Determination and enabling

At present, the FC-TAPE document has two independent mechanisms for
determining the support of precise ordering:

	a)  Process Login negotiates the support of precise ordering using
	    the CRNS (CRN supported) bit.
	   =20
	b)  The FC Control mode page controls the enabling of precise
	    ordering using the ECRN bit.
	   =20
Because of the splendors of the SCSI implementation, this dual enabling
is actually redundant.

The precise ordering function is actually a function that is decided =
upon
and required on a command by command basis for a certain class of =
devices.
As such, it is really a SCSI level functionality, not a Fibre Channel =
level
functionality.  And the SCSI level control function, provided by=20
MODE SENSE/SELECT, is sufficient to properly identify, control, and
enable precise ordering.

Therefore I propose to drop the PRLI CRNS bit.

What remains is the ECRN bit managed by MODE SENSE/SELECT.

Each initiator can talk to its own applications in a vendor specific =
manner
to let the application client know that it supports precise ordering.  =
Of course
this is necessary anyway, since the application client must be capable =
of
instructing the initiator which commands should have precise ordering=20
applied.  The application client then asks the device server of the =
target=20
whether or not the precise ordering capability is supported using the
appropriate MODE SENSE command.  If there is pre-knowledge, it may be
sufficient to ask if the current ECRN bit is one, indicating not only =
that
it is capable of precise ordering, but presently executing it.  If there =
is
no pre-knowledge, the bomb-proof mechanism is to ask the device server =
if
the ECRN bit is changeable.  If it is, the application client can choose =
to
set it or clear it.  If it is not, the application client knows that the
function is not supported.

That all provides a clean, fool-proof, SCSI only mechanism, making the
PRLI CRNS an unnecessary request across some strange architectural =
boundaries.



----------------------------------------------------------------
Bob Snively			     Phone:	  (510) 574-9051
Sun Microsystems Computer Company     =20
Mail Stop NWK 04-104
901 San Antonio Road	             E-mail: bob.snively at sun.com
Palo Alto, CA 94303
----------------------------------------------------------------



*
* For T10 Reflector information, send a message with
* 'info t10' (no quotes) in the message body to majordomo at symbios.com