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

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

Julian,

Thanks for the clarifications. One further question below (that I've asked
in several different ways a couple of times now ;) :

> 2) The READ I/O PDUs do not use a "Target Task Tag".
> The WRITE I/O PDUs use a "Target Task Tag" per R2T
> and not per task.
> 
> It seems like the only unique per I/O identifier is the Initiator
> Task Tag. (?) Is it the intention of iSCSI that targets should be
> using the Initiator Task Tag as the per I/O lookup tag ?
> 
> If this is true, then, the name "Initiator Task Tag" is a misnomer
> and it should just be "Task Tag", since it is used by both initiators
> and
> targets.
> <js> We use initiator and target for the task to state who is "generating"
> the tag </js>

Since a READ Data PDU has no Target Task Tag, is it the expectation that
iSCSI targets should perform a lookup on the Initiator Task Tag to obtain
their per-task data structure ? This is a performance penalty, if so.

Again, with WRITE Data PDUs there is no target assigned
per-task tag. While one could argue about vertically encoding the Target
Task Tag and the Target Transfer Tag into the same "Target Transfer Tag",
this would seem like an ugly hack to work around a shortcoming in the PDU
header. It would be desirable to have seperate Target Task Tag fields for
both READ and WRITE Data PDUs.

Thanks,
Santosh 


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