Re: iSCSI : EnableACA

[julian_satran@il.ibm.com]

Santosh - get through every CDB at a reset is not very practical - and I am
afraid it will also be considered bad engineering - you want to clean
everything up as it might be in a mess.

Also the behaviour is inconsistent for commands in flight and those queued
already :

- for those queued already it is ACA if any in the queue is ACA (at least
from your description)
- for those in flight only if the first is ACA

Julo

Santosh Rao <santoshr@cup.hp.com> on 29/04/2001 08:40:44

Please respond to Santosh Rao <santoshr@cup.hp.com>

To:   Julian Satran/Haifa/IBM@IBMIL
cc:   santoshr@hpcuhe.cup.hp.com (Santosh Rao)
Subject:  Re: iSCSI : EnableACA




Julian,

The point I'm trying to make is that if there were no prior NACA I/Os
in the task set, those I/Os had no ordering dependencies. In that case,
ACA is not required. CAC is sufficient.

In the case where ordering of I/Os is required, such I/Os expect ACA to be
established on an error and they have their NACA bit set.

IOW,
1) no NACA in task set => no ordering required => use CAC on error

2) NACA in task set => some I/Os require ordering => use ACA on error

3) First NACA I/Os arrive after CAC => process normally (I/Os prior to CAC
did not expect ordering).

The above is all based on the fundamental model that I/Os that expect
ordering MUST set the NACA bit in their CDBs. Hence, ACA is not required
to be established when the task set does not contain a NACA I/O.

Regards,
Santosh

>
> Sure - the unit attention is cleared by the first and all the others get
> true - for non-ACA it is OK
> for ACA we wanted all to be dropte up to explicit reset.
>
> Julo
>
> Santosh Rao <santoshr@cup.hp.com> on 29/04/2001 00:59:42
>
> Please respond to Santosh Rao <santoshr@cup.hp.com>
>
> To:   ips@ece.cmu.edu (ips)
> cc:   Julian Satran/Haifa/IBM@IBMIL
> Subject:  Re: iSCSI : EnableACA
>
>
>
>
> > > What about a command in flight (that
> > > was the first that had a NACA bit)?
> >
> > Such I/Os would be errored back with "ACA Active" SCSI Status.
>
> Oops. I believe your question was regarding the first NACA set CDB
> in-flight and not yet in the task set at the time of the task mgmt cmd.
>
> Such a scenario implies the I/Os prior to that first NACA set I/O would
> have had no ordering constraints. In this case, no ACA is established for
> the task mgmt cmd prior to the first NACA I/O. [CAC is established.]
>
> The CAC is cleared on the next I/O [other than INQUIRY and REPORT LUNS]
> that arrives after CAC was established. Subsequent arrival of a NACA set
> I/O is processed normally and no loss of ordering occurs in this case.
>
> Did I miss something about this scenario (?)
>
> Regards,
> Santosh
>
> --
> #################################
> Santosh Rao
> Software Design Engineer,
> HP, Cupertino.
> email : santoshr@cup.hp.com
> Phone : 408-447-3751
> #################################
>
>
>
>


--
#################################
Santosh Rao
Software Design Engineer,
HP, Cupertino.
email : santoshr@cup.hp.com
Phone : 408-447-3751
#################################