FCP Out of Order Data Delivery

Witalka, Jerome J [RV] jjw1 at PO9.RV.unisys.com
Tue Dec 13 14:22:00 PST 1994


Request for Change to the Fibre Channel Protocol for SCSI (FCP) 
Specification X3T10 993D

My current reading of the FCP specification requires all Initiators to 
support an FCP_XFER_RDY DATA_RO field that specifies out of order data 
delivery (SAM random buffer access).  I believe this is an unacceptable 
burden for those Initiators that are required to support unlimited 
scatter/gather operations.  Our host software is allowed to specify scatter 
gather boundaries of a single main storage word.  Theoretically, we could be 
given a single 1000 byte disk read request that could be mapped to a 200 
entry scatter/gather list specifying 200 different main storage buffer 
locations.  If we had to support out of order data delivery, it could take 
an unacceptable amount of processing time to pour through the scatter/gather 
list and figure out where the starting storage address is for this Data IU 
as opposed to always processing the scatter/gather list sequentially.

Given this, I would like to request a change to FCP to allow an Initiator to 
require in order data delivery (SAM sequential buffer access) for all data 
transfers.  SIP has effectively provided this functionality with the Enable 
Modify Data Pointer (EMDP) bit in the Disconnect/Reconnect mode page.  The 
definition of this bit in the SCSI 3 Primary Commands could be expanded to 
require the FCP_XFER_RDY DATA_RO field specify in order data delivery or a 
new bit could be added to the Process Login FCP Service parameter page to 
require in order data delivery.

                          Jerry Witalka  M.S. 4873
                          Unisys Corporation
                          P.O. Box 64942
                          St. Paul, MN 55164-0942

                          EMail:jjw1 at po9.rv.unisys.com





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