Patent ID: 7054266

Claim:
A virtualization switch being connected with a plurality of storage units and a computer, said switch being connected with said storage units through a plurality of communication paths, comprising: a plurality of interfaces being connected with said storage units or said computer; and an internal switch for connecting said plurality of interfaces with one another; a management table having information about a virtual logical unit number (virtual LUN) of a virtual storage, a LUN, a first communication path of said communication paths, a second communication path of said communication paths, and a data transfer starting information of a command, said virtual LUN being used to virtually represent a position of said LUN in said storage units for said computer and relay a command, sent from said computer to said virtual LUN, to said LUN, said first communication path being used if trouble does not occur in said first communication path and said second communication path being used if trouble occurs in said first communication path; wherein a first interface of said plurality of interfaces receives a command for data transfer from said computer to said virtual storage, records an identifier for identifying said command, transfers said command to said LUN in said storage units through a first communication path of said plurality of communication paths based on said management table, detects, in response to said command , a trouble occurring in said first communication path, records a starting of said data transfer upon said command with said recorded identifier, transmits, if a starting of a data transfer has been recorded, a frame for noticing an error of said received command to said computer if starting of said data transfer has not been recorded, creates a new data transfer upon said command by using said LUN corresponding to said virtual LUN without transmitting said frame for noticing said error and transfers a command to said LUN in said storage units through said second communication path.