Re: iSCSI : Command Ordering Proposal.

[Santosh Rao <santoshr@cup.hp.com>]

Charles Monia wrote:

>   For example, if I
> send commands A B |C| D E, where |C| is ordered, I expect that D and E won't
> complete before |C|.  If A B D and E arrive followed by |C|, there's no way
> to obtain the correct behavior. Incidentally, similar constraints hold true
> for "head of queue" tasks.
>

Charles,

SAM-2 Section 7 states :

"The rules for task set management apply only after the task is entered
into the task set."

This implies that the enforcement of the ordering of task tags in your above
example is NOT based on when the initiator sent the commands, but on when
these tasks enter the task set at the target.

i.e. The initiator may send A, B, |C|, D, E, where |C| is ordered.

The commands may arrive at the target in the order :
A, E, |C|, B, D in a multi-connection session.

The commands A and E are not subject to any form of ordering.
(being simple tag commands and having no ordered tag commands
ahead in the task set.)

The commands |C|, B & D are subject to the ordering that B & D cannot
be executed until C is first executed. Thereafter, B & D are subject to
simple tag rules.

I believe the confusion lies in whether ordered task tags imply end-to-end
ordering or ordering within the received task set at the target. the former
requires strict ordering on the link or re-ordering at the target, in the
absence
of strict link ordering. The latter does NOT require any link ordering or
re-ordering
at the target, since it only enforces ordering within the received task set.

Comments ?

Regards,
Santosh
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