Patent ID: 7913037
Filing Date: 2011-03-22
Classification: G06F

Abstract:
1. 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 an 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 a plurality of SAS expander devices, comprising at least a first SAS expander device and a second SAS expander device, each SAS expander device being connected to at least one SAS target device by a respective physical link which is physical wiring, wherein said first SAS expander device is directly connected to the SAS initiator device by a first wide link constituted by a first plurality of physical links and said first SAS expander device is directly connected to the second SAS expander device by a second wide link, constituted by a second 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 first wide link and the second wide link, said SAS initiator device having a physical-link allocation control section operative to allocate a certain physical link from among the first plurality of physical links constituting the first wide link and to allocate a certain physical link from among the second plurality of physical links constituting the second wide link, wherein each of the first and second SAS expander devices 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 respective SAS expander device, wherein the route table includes identifiers corresponding to the plurality of physical ports and SAS addresses of the target devices indirectly connected at a downstream side of the respective SAS expander device 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 is sent by indicating the SAS address of the wide port of the first SAS expander device, wherein the first 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 the direct device table and the route table stored in the first SAS expander device, selects an available physical port of an upstream side of the first SAS expander device and an available physical port of a downstream side of the first SAS expander device from the plurality of physical ports corresponding to the wide port of the first SAS expander device, defines at least one path including the available physical port of the first SAS expander device and the physical port of the second SAS expander device on an upstream side, and transfers an address frame including the SAS address of the SAS target device by indicating the SAS address of the wide port of the second SAS expander device to the second SAS expander device via the selected available physical port, wherein the second SAS expander device receives the address frame, checks paths from the second SAS expander device to the SAS target device for establishing the connection by referring the direct device table stored in the second SAS expander device, selects an available physical port of a downstream side of the second SAS expander device from the plurality of physical ports connected to the SAS target device, and defines at least one path from the second SAS expander device to the SAS target device, and wherein the physical-link allocation control section selectively controls a number of physical links allocated to a particular target device for at least one wide link among the first wide link between the SAS initiator device and the first SAS expander device and the second wide link, between the first SAS expander device and the second SAS expander device, the selective control being based upon a specified performance of the SAS target devices related to the wide link, and updates the direct device table and the route table on the basis of the allocation.