Logical unit groups and optional target reset

Ralph Weber ralphoweber at CompuServe.COM
Thu Dec 21 17:06:26 PST 2000

* From the T10 Reflector (t10 at t10.org), posted by:
* Ralph Weber <ralphoweber at compuserve.com>

} We could change SAM-2 to let command sets dictate, so
} new command sets like SBC-2 and SSC-2 could mark it as
} optional.  However, command set standards don't normally
} deal with task management features.

The mail announcing this proposal suggested that changing
SAM-2 would allow protocol standards to decide whether
TARGET RESET is mandatory, and I had no problems with that.
I assume(d) that SPI, FCP, and other predominately storage
protocols would continue to require TARGET RESET support,
whereas iSCSI and such like would make it optional or even
prohibit it.

This is appropriate because protocols such as iSCSI may have
a great deal more than storage transactions riding on an
interconnect and a TARGET RESET could be a very bad thing
in some such environments.

However, I have serious problems with making the TARGET
RESET decision in the command set standards.  It is the
nature of the transport protocol that reflects on the
presence of non-storage traffic on the interconnect and
thus the appropriateness of TARGET RESET.

As noted above, I would oppose making TARGET RESET mandatory
in any strictly or predominately storage protocol because it
is a tool that most current storage protocol drivers use to
some level of beneficial effect.  But, where storage is not
the predominate  traffic on the protocol bus, TARGET RESET
may simply be too big a hammer, at least as we understand
the concept today.

I think the proposal that SBC-2 or any other command set
standard should discuss the implementation of TARGET RESET
(or any other task management function for that matter)
is wrong.  To do so almost certainly would result in
misdirected requirements for or against the presence of
TARGET RESET.  It's a protocol not a command set issue.



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