Reducing write i/o latency using asynchronous fibre channel exchange

Abstract

Methods and systems are provided for Reducing Write I/O Latency Using Asynchronous Fibre Channel Exchange. A FCP target device may send one or more FC write control information units (IUs) to a FCP initiator device within a first FC exchange to request a transfer of data associated with a FCP write command IU previously sent to the FCP target device by the FCP initiator device within a second FC exchange. The FC write control IUs may be sent without the FCP target device first receiving from the FCP initiator device a sequence initiative of the second FC exchange, and/or may be sent within the first FC exchange concurrently with the FCP initiator device sending one or more FCP data IU sequences within the second FC exchange to the FCP target device. Thus, a full-duplex communication environment may be setup between the FCP initiator device and FCP target device.

We claim:  
     
         1 - 20 . (canceled) 
     
     
         21 . A system, comprising:
 a Fibre Channel (FC) Protocol for SCSI (FCP) target device comprising at least a processor, wherein the FCP target device is operable to:
 send one or more FC write control information units (IUs) to a FCP initiator device within a first FC exchange to request a transfer of data associated with a FCP write command IU previously sent to the FCP target device by the FCP initiator device within a second FC exchange; 
 wherein the FC write control IUs are sent without the FCP target device first receiving from the FCP initiator device a sequence initiative of the second FC exchange. 
   
     
     
         22 . The system of  claim 21 , wherein the FCP target device is operable to send the one or more write control IUs within the first FC exchange concurrently with the FCP initiator device sending one or more FCP data IU sequences within the second FC exchange to the FCP target device. 
     
     
         23 . The system of  claim 21 , wherein the FCP target device is operable to send a second one or more write control IUs to the FCP initiator device 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 device by the FCP initiator device within a third FC exchange;
 wherein the first FC exchange is distinct from the third FC exchange.   
     
     
         24 . The system of  claim 21 , wherein the payload of each write control IU of the one or more write control IUs comprises one or more of: an originator exchange identifier (OX_ID) value with which the FCP initiator originated the second FC exchange, a responder exchange identifier (RX_ID) value assigned by the FCP target for the second FC exchange, and an indicator that instructs the FCP initiator device whether to hold or transfer the sequence initiative of the second FC exchange to the FCP target device. 
     
     
         25 . The system of  claim 21 , 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. 
     
     
         26 . The system of  claim 21 , 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. 
     
     
         27 . The system of  claim 21 , wherein the one or more write control IUs hold a sequence initiative of the first FC exchange. 
     
     
         28 . A system, comprising:
 a Fibre Channel (FC) Protocol for SCSI (FCP) initiator device comprising at least a processor, wherein the FCP initiator device is operable to:
 receive one or more FC write control information units (IUs) from a FCP target device within a first FC exchange requesting a transfer of data associated with a FCP write command IU previously sent to the FCP target device by the FCP initiator device within a second FC exchange; 
 wherein the FC write control IUs are received without the FCP initiator device first sending a sequence initiative of the second FC exchange. 
   
     
     
         29 . The system of  claim 28 , wherein the FCP initiator device 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 device. 
     
     
         30 . The system of  claim 28 , wherein the FCP initiator device is operable to receive a second one or more write control IUs from the FCP target device within the first FC exchange requesting a transfer of data associated with a second FCP write command IU previously sent to the FCP target device by the FCP initiator device within a third FC exchange;
 wherein the first FC exchange is distinct from the third FC exchange;   
     
     
         31 . The system of  claim 28 , wherein the payload of each write control IU of the one or more write control IUs comprises one or more of: an originator exchange identifier (OX_ID) value with which the FCP initiator device originated the second FC exchange, a responder exchange identifier (RX_ID) value assigned by the FCP target device for the second FC exchange, an indicator that instructs the FCP initiator device whether to hold or transfer the sequence initiative of the second FC exchange to the FCP target device. 
     
     
         32 . The system of  claim 28 , 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. 
     
     
         33 . The system of  claim 28 , 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. 
     
     
         34 . The system of  claim 28 , wherein the one or more write control IUs hold a sequence initiative of the first FC exchange. 
     
     
         35 . The system of  claim 28 , wherein the FCP write command IU sent to the FCP target device by the FCP initiator device holds the sequence initiative of the second FC exchange. 
     
     
         36 . A method, comprising:
 sending, by a Fibre Channel (FC) Protocol for SCSI (FCP) target device, one or more FC write control information units (IUs) to an FCP initiator device within a first FC exchange to request a transfer of data associated with a FCP write command IU previously sent to the FCP target device by the FCP initiator device within a second FC exchange;   wherein the FC write control IUs are sent without the FCP target device first receiving from the FCP initiator device a sequence initiative of the second FC exchange.   
     
     
         37 . The method of  claim 36 , comprising sending the one or more write control IUs within the first FC exchange concurrently with the FCP initiator device sending one or more FCP data IU sequences within the second FC exchange to the FCP target device. 
     
     
         38 . The method of  claim 36 , 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. 
     
     
         39 . The method of  claim 36 , 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. 
     
     
         40 . The method of  claim 36 , wherein the one or more write control IUs hold a sequence initiative of the first FC exchange.