Re: iSCSI: Recognizing Recovery R2Ts

["Mallikarjun C." <cbm@rose.hp.com>]

> The question is how does an initiator know when a R2T is a recovery
> R2T and not a normal R2T?  The case I am referring is in regard to the
> last paragraph in section 9.8 of iSCSI-v17-working:
> 
> "DataSequenceInOrder governs the buffer offset ordering in consecutive 
>  R2Ts. If DataSequenceInOrder is Yes, then consecutive R2Ts MUST refer 
>  to continuous non-overlapping ranges except for Recovery-R2Ts."
> 
> So the initiator is allowed to ignore the buffer offset in the case of 
> DataSequenceInOrder=Yes when receiving a Recovery R2T,  but how does the
> initiator know in fact an R2T is being used for within-command
> recovery?  AFAICS there is no "Recovery bit" in the R2T pdu,  and am at
> a loss as to how the initiator would reliably ascertain this situation.

An operational ErrorRecoveryLevel>=1 and DataSequenceInOrder=Yes 
is assumed for this discussion.

- Generally from the initiator's perspective, any R2T with a "Buffer Offset"
  that's seeking some data that the initiator already transmitted as Data-Out 
  is a recognizable recovery R2T. 

- While the target may be generating a "recovery R2T" in some cases, the 
   initiator may not recognize it as such because the earlier R2T was lost for
   the initiator. 
--
Mallikarjun

Mallikarjun Chadalapaka
Networked Storage Architecture
Network Storage Solutions
Hewlett-Packard MS 5668 
Roseville CA 95747
cbm@rose.hp.com