Computer system for controlling allocation of physical links and method thereof

A computer system comprising:

• a plurality of Serial Attached SCSI (SAS) target devices, constituting targets that follow the SAS protocol;
• a SAS initiator device, constituting a SAS initiator that follows the SAS protocol, that is connected to a host computer accessing data stored in the plurality of SAS target devices;
• and
• an SAS expander device, the SAS expander device being connected to at least one SAS target device by a respective physical link which is physical wiring,
• wherein the SAS expander device is directly connected to a SAS initiator device by a wide Link constituted by a plurality of physical links via a wide port constituting a plurality of physical ports each corresponding to a respective physical link,
• wherein the SAS initiator device is operative to selectively establish connections between the host computer and the plurality of SAS target devices via the physical links in the wide link,
• wherein the SAS expander device has a direct device table and a route table,
• wherein the direct device table includes identifiers corresponding to the plurality of physical ports related to the SAS address corresponding to the wide port, SAS addresses of the target devices directly attached to the physical ports, SAS addresses of the target devices that permit transmission of a connection request, on a physical port basis, and information related to upstream and downstream wide links for the SAS expander device,
• wherein the route table includes identifiers corresponding to the plurality of physical ports and SAS addresses of the target devices connected to an SAS target device,
• wherein the SAS initiator device is operative to send open address frames to one of the SAS target devices to establish a connection for accessing data stored in the SAS target device according to the SAS protocol and the open address frames are sent by indicating the SAS address of the wide port of the SAS expander device,
• wherein the SAS expander device receives the open address frames including the SAS address of the SAS target device,
• checks paths from the SAS initiator device to the SAS target device for establishing the connection by referring to the direct device table and the route table stored in the SAS expander device,
• selects an available physical port of an upstream side of the SAS expander device and an available physical port of a downstream side of the SAS expander device from the plurality of physical ports corresponding to the wide port of the SAS expander device or connected to the SAS target device,
• defines at least one path including the available physical port of an upstream side of the SAS expander device and the physical port of a downstream side of the SAS expander device, and
• transfers an address frame including the SAS address of the SAS target device by indicating the SAS address of the wide port from a host computer to the SAS target device via the selected available physical port.