SAS Paired subtractive routing

A system, comprising:

• means for assigning an input port to a SAS expander device;
• means for assigning an output port to the SAS expander device;
• means for defining the output port and the input port to be paired with each other as a primary subtractive port;
• means for programming only a SAS initiator address in the route table of the SAS expander;
• means for sending an OPEN command out the output port upon receiving the OPEN command into the input port if the DEST of the OPEN command is not a direct attached device of the SAS expander device and the DEST is not in the route table of the SAS expander device;
• and
• means for sending an OPEN command out the input port upon receiving the OPEN command into the output port if the DEST of the OPEN command is not a direct attached device of the SAS expander device and the DEST is not in the route table of the SAS expander device.

A computer-readable medium having computer-executable instructions for performing a method for performing paired subtractive routing in a Serial Attached Small Computer System Interface (SAS) cascaded topology, the method comprising:

• assigning an input port to a SAS expander device;
• assigning an output port to the SAS expander device;
• defining the output port and the input port to be paired with each other as a primary subtractive port;
• programming only a SAS initiator address in the route table of the SAS expander;
• sending an OPEN command out the output port upon receiving the OPEN command into the input port if the DEST of the OPEN command is not a direct attached device of the SAS expander device and the DEST is not in the route table of the SAS expander device;
• and
• sending an OPEN command out the input port upon receiving the OPEN command into the output port if the DEST of the OPEN command is not a direct attached device of the SAS expander device and the DEST is not in the route table of the SAS expander device.