RE: ISCSI: Urgent Flag requirement violates TCP.

[Black_David@emc.com]

> I think software has to deal with it anyway.  Let's use your scenario,
except
> take the case where nothing is dropped or re-ordered.  What's to say that
the
> disc drive has to complete A before it completes B (the abort)?  What if
it just
> immediately acknowledges the abort, then cleans up and sends the
completion for A?

A disk drive that does that strikes me as broken.  Abort means abort - to
claim that
a command could not be aborted and then complete it successfully sounds like
a bug, not a feature.

> > FWIW, this can't happen in Fibre Channel because the completion of A
won't
> > be retransmitted.
> 
> It won't be retransmitted, but it could get re-ordered in the FC traffic,
so the
> FC software/firmware also has to deal with it.

Not likely.  On a single connection, there is virtually no FC switchgear out
there
that will reorder frames.  Given the increasing scale of FC, we'll doubtless
see
routing update effects among FC switches that will lead to reordering in a
fashion
similar to IP, but one just does not see reordered FC frames in current
deployments
due to conservatism about both scale and configuration management.

What's the gain from introducing this additional non-determinism to the
system?

--David

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David L. Black, Senior Technologist
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