FCP-2 problem

Baldwin, Dave Dave.Baldwin at emulex.com
Wed Jun 14 13:49:08 PDT 2000

* From the T10 Reflector (t10 at t10.org), posted by:
* "Baldwin, Dave" <Dave.Baldwin at emulex.com>
Neil and Terence,

I had kicked this idea around too. This makes it better, but not perfect. The
issue I came up with is:

If the FCP_CONF and the second command are dropped, you have the same problem.
The REC will end up recovering the first command, while the initiator thinks the
second command has been completed.

Best regards,
Dave Baldwin

"Neil T. Wanamaker" wrote:

> At 02:57 PM 6/14/00 -0400, Terence Kelleher wrote:
> >*
> >* From the fc reflector, posted by:
> >* "Terence Kelleher" <terryk at pathlight.com>
> >*
> >Does use of FCP_CONF_REQ on the response resolve the issue? The target will
> >release the resource after receiving FCP_CONF and the OXID is free. The REC
> >sent after the lost command will then not receive an ACC, as the OXID is
> >invalid.
> >
> >CMD OXID = 1 ----->
> >
> >                <----- FCP_RSP with FCP_CONF_REQ
> >
> >FCP_CONF     ----->
> >
> >CMD OXID = 1 ---X
> >
> >REC          ----->
> >
> >                <----- LS_REJ
> >
> >
> >If the FCP_CONF is lost, the target would issue REC to request
> >retransmission. If the OXID is reused before FCP_CONF is delivered to the
> >target, the Command is rejected because the OXID refers to an exchange which
> >is still open.
> >
> The use of FCP_CONF will make things better, in that there will not be an
> ambiguity.
> As long as messages must be passed between initiator and target, there are
> windows during which the two are in different states. With FCP_CONF, the
> exchange can be closed first by the target (as in FCP(-1)). Even if the
> initiator closes the exchange before receiving confirmation that the target
> has received the FCP_CONF (and the initiator re-uses the OX_ID), the
> behavior is benign, because the target can reject the new command if the
> FCP_CONF was lost; the initiator can then reissue the command with a new
> OX_ID, the target can age out the old exchange, and everybody's happy.

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