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

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

Raghavendra Rao wrote:

> > Again, with WRITE Data PDUs there is no target assigned
> > per-task tag. While one could argue about vertically encoding the Target
>
> There is - this is done during R2T time and every solicited data PDU
> from the initiator goes out with this tag.

The "Target Transfer Tag" that you are referring to is per R2T and not per task.
There is no per-task identifier that can be used by the targets to track the
task. They will either have to :

a) use the Initiator Task Tag

or

b) resort to some form of vertical encoding of the Target Task Tag (a per-task
target id) into the Target Transfer Tag (the PDU defined per-R2T target id).

(a) has perofrmance impacts.
(b) is an ugly implementation-specific kludge and also reduces the Target Task
Tag space due to the vertical encoding of 2 fields into the 32-bit space.

Thanks,
Santosh
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