iSCSI ACA requirement

["Dave Peterson" <dap@cisco.com>]

I'm having heartburn with the statement in iSCSI rev 10 clause 9.2:
"As iSCSI can have many commands in-flight between initiator and target,
iSCSI mandates support for ACA."

My understanding of the above statement is that iSCSI target must indicate
support for NACA=1.

Requiring ACA is problematic and normally not necessary for implementations
for a variety of reasons.
Examples:
a. A small number of devices actually support NACA=1.
b. In practice FC applications do not require command ordering (i.e., use of
the Simple Queue Tag). If ordering is a consideration the application will
issue the command and wait for the response.
c. The FC/FCP standards do not require NACA=1.
d. Complicates bridging implementations
	- bridge must proxy NACA=1 for a device that does not support NACA=1
	- bridge must maintain NACA behavior when the end device does not support
NACA=1

I do understand the benefits to requiring NACA=1 especially when command
ordering and stateful operations are desired, but its not realistic at this
time, IMHO.
As such this use of ACA should be a SHOULD, not a must or mandate.

Dave