Reducing write I/O latency using asynchronous Fibre Channel exchange
View Patent ↗A FCP initiator sends a FCP write command to a FCP target within a second FC Exchange, and the target sends one or more FC write control IUs to the initiator within a first FC Exchange to request a transfer of data associated with the write command. The first and second FC exchanges are distinct from one another. A payload of each write control IU includes an OX_ID value with which the initiator originated the second Exchange and a RX_ID value assigned by the FCP target for the second exchange. The two Exchanges yield a full-duplex communication environment between the initiator and target that enables the reduction or elimination of latencies incurred in a conventional FCP write I/O operation due to the half-duplex nature of a single FC Exchange. The write control IU may be an enhanced FCP_XFER_RDY IU or a new FC IU previously undefined by the FCP standard.
1. A Fibre Channel (FC) Protocol for SCSI (FCP) target, comprising:
a FC port; and
a processor, adapted to communicate with a FCP initiator via the FC port;
wherein the FCP target is configured to send one or more FC write control information units (IUs) to the FCP initiator within a first FC exchange to request a transfer of data associated with a FCP write command IU previously sent to the FCP target by the FCP initiator within a second FC exchange, without the FCP initiator first sending its sequence initiative in the second FC exchange;
wherein the first FC exchange is distinct from the second FC exchange;
wherein a payload of each of the one or more write control IUs comprises:
an originator exchange identifier (OX_ID) value with which the FCP initiator originated the second FC exchange; and
a responder exchange identifier (RX_ID) value assigned by the FCP target for the second FC exchange.
2. The FCP target of claim 1 , wherein the FCP target is configured to send the one or more write control IUs within the first FC exchange concurrently with the FCP initiator sending one or more FCP data IU sequences within the second FC exchange to the FCP target.
3. The FCP target of claim 1 , wherein the FCP target is further configured to send a second one or more write control IUs to the FCP initiator within the first FC exchange to request a transfer of data associated with a second FCP write command IU previously sent to the FCP target by the FCP initiator within a third FC exchange;
wherein the first FC exchange is distinct from the third FC exchange;
wherein a payload of each of the second one or more write control IUs comprises:
an OX_ID value with which the FCP initiator originated the third FC exchange; and
a RX_ID value assigned by the FCP target for the third FC exchange.
4. The FCP target of claim 1 , wherein the payload of each write control IU of the one or more write control IUs further comprises: an indicator that instructs the FCP initiator whether to hold or transfer sequence initiative of the second FC exchange to the FCP target.
5. The FCP target of claim 1 , wherein each write control IU of the one or more write control IUs comprises a new FCP IU previously undefined by the FCP-4 standard.
6. The FCP target of claim 1 , wherein each write control IU of the one or more write control IUs comprises an enhanced FCP transfer ready (FCP_XFER_RDY) IU, wherein the payload of the write control IU is located in bits previously reserved by the FCP-4 standard.
7. The FCP target of claim 1 , wherein the one or more write control IUs hold sequence initiative of the first FC exchange.
8. A Fibre Channel (FC) Protocol for SCSI (FCP) initiator, comprising:
a FC port; and
a processor, adapted to communicate with a FCP target via the FC port;
wherein the FCP initiator is configured to receive one or more FC write control information units (IUs) from the FCP target within a first FC exchange requesting a transfer of data associated with a FCP write command IU previously sent to the FCP target by the FCP initiator within a second FC exchange, without the FCP initiator first sending its sequence initiative in the second FC exchange;
wherein the first FC exchange is distinct from the second FC exchange;
wherein a payload of each of the one or more write control IUs comprises:
an originator exchange identifier (OX_ID) value with which the FCP initiator originated the second FC exchange; and
a responder exchange identifier (RX_ID) value assigned by the FCP target for the second FC exchange.
9. The FCP initiator of claim 8 , wherein the FCP initiator is configured to receive the one or more write control IUs within the first FC exchange concurrently with sending one or more FCP data IU sequences within the second FC exchange to the FCP target.
10. The FCP initiator of claim 8 ,
wherein the FCP initiator is further configured to receive a second one or more write control IUs from the FCP target within the first FC exchange requesting a transfer of data associated with a second FCP write command IU previously sent to the FCP target by the FCP initiator within a third FC exchange;
wherein the first FC exchange is distinct from the third FC exchange;
wherein a payload of each of the second one or more write control IUs comprises:
an OX_ID value with which the FCP initiator originated the third FC exchange; and
a RX_ID value assigned by the FCP target for the third FC exchange.
11. The FCP initiator of claim 8 , wherein the payload of each write control IU of the one or more write control IUs further comprises: an indicator that instructs the FCP initiator whether to hold or transfer sequence initiative of the second FC exchange to the FCP target.
12. The FCP initiator of claim 8 , wherein each write control IU of the one or more write control IUs comprises a new FCP IU previously undefined by the FCP-4 standard.
13. The FCP initiator of claim 8 , wherein each write control IU of the one or more write control IUs comprises an enhanced FCP transfer ready (FCP_XFER_RDY) IU, wherein the payload of the write control IU is located in bits previously reserved by the FCP-4 standard.
14. The FCP initiator of claim 8 , wherein the one or more write control IUs hold sequence initiative of the first FC exchange.
15. The FCP initiator of claim 8 , wherein the FCP write command IU sent to the FCP target by the FCP initiator holds sequence initiative of the second FC exchange.
16. A method, comprising:
sending, by a Fibre Channel (FC) Protocol for SCSI (FCP) target, one or more FC write control information units (IUs) to an FCP initiator within a first FC exchange to request a transfer of data associated with a FCP write command IU previously sent to the FCP target by the FCP initiator within a second FC exchange, without the FCP initiator first sending its sequence initiative in the second FC exchange;
wherein the first FC exchange is distinct from the second FC exchange;
wherein a payload of each of the one or more write control IUs comprises:
an originator exchange identifier (OX_ID) value with which the FCP initiator originated the second FC exchange; and
a responder exchange identifier (RX_ID) value assigned by the FCP target for the second FC exchange.
17. The method of claim 16 , wherein said sending the one or more write control IUs within the first FC exchange is performed concurrently with the FCP initiator sending one or more FCP data IU sequences within the second FC exchange to the FCP target.
18. The method of claim 16 , wherein each write control IU of the one or more write control IUs comprises a new FCP IU previously undefined by the FCP-4 standard.
19. The method of claim 16 , wherein each write control IU of the one or more write control IUs comprises an enhanced FCP transfer ready (FCP_XFER_RDY) IU, wherein the payload of the write control IU is located in bits previously reserved by the FCP-4 standard.
20. The method of claim 16 , wherein the one or more write control IUs hold sequence initiative of the first FC exchange.