RE: iSCSI : On the subject of R2T and Task Tags.

["Douglas Otis" <dotis@sanlight.net>]

Venkat,

You misunderstood my comment.  Matt had indicated a simple solution of
counting bytes.  As you indicate, the target tag is uncertain.  Assumptions
about data not overlapping is also incorrect and data overlays may not be
sent in sequence.  All of this adds to difficulty in confirming completion
before returning to the application.

Doug

> Doug,
>
> The draft make should not make any statements about how a target
> chooses to
> assign Target Task Tags. Some may choose to assign it per R2T, others may
> choose to assign it per task, based on how they choose to implement the
> target. Since the initiator is required to reflect it, I do not believe
> there are any interoperability issues. If an implementation wishes to do a
> Task-SubTask breakdown, they can choose to partition the 32 bits into
> portions that can be used for identifying resources within the target.
>
> Venkat Rangan
> Rhapsody Networks Inc.
> http://www.rhapsodynetworks.com
>
>
> -----Original Message-----
> From: owner-ips@ece.cmu.edu [mailto:owner-ips@ece.cmu.edu]On Behalf Of
> Douglas Otis
> Sent: Wednesday, January 10, 2001 5:27 PM
> To: Matt Wakeley; IPS Reflector
> Subject: RE: iSCSI : On the subject of R2T and Task Tags.
>
>
> Matt,
>
> With independent error checking requiring an additional level of error
> handling requesting repeated reads, there could be old responses combined
> with the retry from failed data digests. (If requesting
> overlapped reads are
> prohibited, retry is an exception.) Without some means of
> identifying which
> retry phase data is associated, a complete set would be difficult to
> confirm.  As order of each data portion is not mandated and these
> transfers
> themselves may overlap, byte counts can not reveal completion.
> Should does
> not mean 'must.'
>
> Doug
>
> > Pierre Labat wrote:
> >
> > > I agree that the draft must not impose to the target to have a
> > different tag
> > > for each R2T (it is up to the target implementation to decide).
> >  I disagree
> > > to impose a unique target tag for the whole IO.  It imposes the
> > target to do
> > > score boarding
> > > to know when all the data have been received. Letting the
> > possiblility to the
> > > target
> > > to have one tag per R2T (or add a subtag identifying the R2T as
> > proposed Santosh)
> > >
> > > allows the target to dispense with the score boarding. The
> > target knows that all
> > > the
> > > data has been received when a data PDU with the "F" bit set has
> > been received
> > > for each R2T.
> >
> > There is no need to do scoreboarding.  Just count the number of bytes
> > received.  If they all add up, then you've received all the data.
> >  I for one
> > would not rely on a PDU with the "F" bit set.  I would want to
> > cross check it
> > with the correct number of bytes.
> >
> >
> > >
> > > Regards,
> > >
> > > Pierre
> > >
> > > >
> > > >
> > -Matt Wakeley
> > Agilent Technologies
> >
>
>
>