Patent ID: 7089359

Claim:
A computer system comprising a computer, a plurality of storage units each containing one or more volumes for storing data used by the computer, and a management computer for managing the status of the plurality of storage units, comprising: one or more first-level storage units each containing one or more first volumes, each of said first volumes being a target volume of an access sent from the computer via a fibre channel interface, and said one or more first volumes having at least one virtual volume, a plurality of second-level storage units, each of which is connected through a fibre channel network to, and hierarchically linked to, one of the first-level storage units, said second-level storage units containing one or more second volumes, wherein each of said second volumes can be a target volume of an access sent from the computer via a fibre channel interface, wherein said one or more first-level storage units are arranged to receive data access requests from said computer to said virtual volume, and to relay said data access requests to at least one of said second volumes based on a relationship between said virtual volume and said at least one second volume that corresponds to said virtual volume, such that said virtual volume as accessed by said computer is transparent as to its relationship to said at least one second volume, volume information collecting means for collecting volume information on the total capacity of each of said first and second volumes contained in the first-level and the second-level storage units, respectively, virtualization information collecting means for collecting virtualization information on the relationships between said virtual volume and said at least one second volume, and effective capacity calculating means for calculating the total effective capacity of the volumes of the first-level and second-level storage units based on subtracting the capacity of the virtual volume from the total capacity of said first and second volumes by using the volume information and the virtualization information thus collected.