Computer system for controlling allocation of physical links and method thereof

A SAS expander device connected to one or more SAS target device in a physical link that is physical wiring or connected to an SAS initiator device in a wide link constituted by a plurality of physical links or connected to another SAS expander device in the wide link, wherein the one or more SAS target devices are targets according to SAS protocol, the SAS initiator device is an initiator in accordance with the SAS protocol, which is connected to a host computer accessing data stored in the one or more SAS target devices,

• the SAS expander device, comprising:
• at least one wide port, said wide port having a respective SAS address allocated thereto and comprising a plurality of physical ports each connected to a plurality of physical links that comprise a wide link and each being identified by a respective physical communication port ID;
• a storage area storing a first switch control information and a second switch control information;
• a physical link allocation control unit controlling allocation to each of the plurality of SAS target devices in a plurality of physical links constituting the wide link,
• wherein the first switch control information includes SAS address of a device directly connected to each physical port for each physical port and SAS address of a device that is allowed to send I/O request or connection establishment request via each physical port,
• wherein the second switch control information includes SAS address of a device connected via at least one other physical port to each physical port for each physical port,
• wherein when a plurality of SAS expanders are connected, the plurality of SAS expander devices are cascade-connected with the SAS expander device connected to the SAS initiator device in the leading position by the wide link,
• wherein the SAS expander device is operative to selectively establish connection between the SAS initiator device and the one or more SAS target devices via a plurality of physical links in the wide link,
• wherein the SAS expander device is operative to send I/O request received form the SAS initiator device to the SAS target device via the established connection,
• wherein the I/O request is sent via a physical link allocated to the SAS target device and cannot pass a physical link that is not allocated to the SAS target device
• wherein each SAS expander device is configured, when an initiator device or a target device issues a predetermined frame for establishing a connection via an open address frame, to refer to expander tables using a transmitting target SAS address as a destination written in the open address frame, and to identify an enabled physical link in the wide port, and
• wherein each SAS expander device is configured to select a physical link having not established a connection among the enabled physical links, and to establish a connection as for the selected physical link.