Re: iSCSI linked commands

[Ralph Weber <ralphoweber@compuserve.com>]

Julian,

julian_satran@il.ibm.com wrote:

> Doug,
>
> I think you would want to go back to SAM.  Linked command are broken by any
> "irregularity" in execution.

The specific statement you are looking for appears on SAM-2 r16
top of PDF page 66, "The receipt of any status, except INTERMEDIATE
or INTERMEDIATE-CONDITION MET, shall indicate that the associated
task has ended."

> The basic assumption is that the initiator is in charge of shipping linked
> commands - one-by-one.

I am not an expert on linked commands (there are only three such
people that I know of).  However, my understanding is that linked
commands are REQUIRED to be shipped one-by-one.  The initiator is
allowed to pick the next linked command based on the results
returned by the previous linked command.

> I assume that for high latency links they won't be very popular.

They are not very popular, period.

> At a very early stage (about 2 years ago) we contemplated the idea of
> "prefetching" linked commands and have the target
> effect the serialization. We would have had to come up with a way of
> conveying the initiator which command broke the chain (if it broke) or
> caused a unit attention (if it caused) and it was not at all clear that
> this was "in the spirit of SAM" .
> There where also more esoteric issues with later command getting modified
> by execution of prior commands etc. -:).

Like I said above, I think pre-fetching linked commands violates
"the rules".

Thanks.

Ralph...