RE: iSCSI: Recognizing Recovery R2Ts

[Black_David@emc.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,

No, the initiator is *never* allowed to ignore the buffer offset.  An
R2T *always* describes the data that the Target wants transferred.

> 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.

A Recovery R2T is a retry of part or all of some previous R2T.
Whether the initiator knows this depends on whether it saw the
previous R2T.  The initiator's behavir should not be affected -
it is supposed to respond to R2Ts (including retries, as allowed
by DataSequenceInOrder - see Section 11.19) until the target gets
all the data it wants and issues a SCSI Response.

Thanks,
--David
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David L. Black, Senior Technologist
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