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

["Venkat Rangan" <venkat@rhapsodynetworks.com>]

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
>