System and method for using a multipath

A Serial Attached SCSI (SAS) expander device configured to connect a SAS initiator and a SAS target, the device comprising:

• a storage unit configured to store, for each of a plurality of paths to the SAS target, a data transfer amount, wherein the data transfer amount is an amount of data transferred between the SAS initiator and the SAS target through said path;
• a receiving unit configured to receive a Serial SCSI Protocol (SSP) command frame from the SAS initiator;
• and
• a determination unit configured to select one path from the plurality of paths to the SAS target to satisfy the SSP command frame and achieve load distribution;
• and
• a transmitting unit configured to transmit the SSP command frame to the SAS target through the selected-path.

A method for using a multipath in a device functioning as a Serial Attached SCSI (SAS) expander configured to connect a SAS initiator and a SAS target, wherein the method comprises the steps of:

• storing for each of a plurality of paths to the SAS target, a data transfer amount, wherein the data transfer amount is an amount of data transferred between the SAS initiator and the SAS target through said path;
• receiving a Serial SCSI Protocol (SSP) command frame from the SAS initiator, wherein the SSP command frame includes a data length amount for data requested to be transferred between the SAS initiator and the SAS target;
• upon receipt of the SSP command frame, selecting one path from the plurality of paths to the SAS target to satisfy the SSP command frame and achieve load distribution;
• adding the data length amount to the data transfer amount for the selected path;
• transmitting the SSP command frame to the SAS target through the selected path;
• receiving an SSP response frame responding to the SSP command frame from the SAS target;
• upon receipt of the SSP response frame, subtracting the data length amount from the data transfer amount for the selected path;
• and
• transmitting the SSP response frame to the SAS initiator.

A computer program product on a computer-readable medium for use as a Serial Attached SCSI (SAS) expander configured to connect a SAS initiator and a SAS target, the computer program product comprising:

• instructions for storing, for each of a plurality of paths to the SAS target, a data transfer amount, wherein the transmitted-received data amount is an amount of data transferred between the SAS initiator and the SAS target through said path;
• instructions for receiving a Serial SCSI Protocol (SSP) command frame from the SAS initiator, wherein the SSP command frame includes a data length amount for data requested to be transferred between the SAS initiator and the SAS target;
• instructions for, upon receipt of the SSP command frame, selecting one path from the plurality of paths to the SAS target to satisfy the SSP command frame and achieve load distribution;
• instructions for adding the data length amount to the data transfer amount for the selected path;
• instructions for transmitting the SSP command frame to the SAS target through the selected path;
• instructions for receiving an SSP response frame responding to the SSP command frame from the SAS target;
• instructions for, upon receipt of the SSP response frame, subtracting the data length amount from the data transfer amount for the selected path;
• and
• instructions for transmitting the SSP response frame to the SAS initiator.