I please ask you to discuss in the FCP-4 WG the possibility to mandate continuous increasing SEQ_CNT in FCP-4. Relying on it greatly simplifies the detection of a missing Sequence and consequently simplifies error recovery, but today is optional in FCP-x (while is mandated by IP over FC and is going to be mandated by FC-SATA).

Additional items for FCP-4 discussion follows (all due to doubts submitted to me...):

- Bidirectional Commands: I think we need to count bytes for both data-in and data-out. Which of these two counters should be put in the FC4VALUE field of the REC ELS?

- Data Overlay: the FCP-3 definition of data overlay says "see SAM-3", but SAM-3 says nothing on data overlay.

- Data Overlay: In which way could it be possible detecting a missing Sequence when data overlay is used and continuously increasing SEQ_CNT is not used? (it seems to us that there is no way, but others may have a different opinion...).

- Data Overlay: how can the FC4VALUE counters can be accurate when data overlap (i.e., how to avoid to count twice the overlapping data)?

The members of the working group came to no real concensus/resolution per the questions and would like to open up the discussion to the T10/T11 commitees, specifically making Continuously Increasing SEQ_CNT a requirement for FCP-4.

We have discussed requiring Continuously Increasing SEQ_CNT during each previous FCP-x standard development efforts and folk opted to not specify it as a requirement since some vendors did not yet fully support it. We may have now moved past that issue.

FCP-3 states: "Sequence level error recovery as described in 12.4 shall not be used for bidirectional SCSI commands." So the question regarding the FC4VALUE field is moot until if/when we want to support FCP-x error detection and recovery for bidirectional commands.

The reference to SAM-3 is not intended to refer the reader to SAM-3 for data overlay, but since it is outside the sentence this is what it means. The reference will be removed since it provides value in this context (i.e., the intent was to refer the reader to SAM-3 for application client buffer offset but that is already covered).