A storage system comprising: an external storage device including a plurality of physical devices and a controller arranged to set a logical volume on a memory area of said physical devices; a first virtualization storage device including a plurality of first disk devices, and having a first virtual device configured by the plurality of first disk devices and a first virtual volume (163, 1E); and a second virtualization storage device including a plurality of second disk devices, and having a second virtual device configured by the plurality of second disk devices and a second virtual volume (163, 2E); wherein said first virtual volume (163, 1E) is connected to said logical volume, and a first path from a host computer to said first virtual volume (163, 1E) which is accessible by said host computer is defined, wherein said second virtualization storage device is arranged to: acquire information regarding said logical volume in said external storage device from said first virtualization storage device, connect said logical volume, which is detected based on said acquired information, to said second virtual volume (163, 2E) of said second virtualization storage device, and define a second path from said host computer to said second virtual volume (163, 2E) using a same identification number for said second virtual volume (163, 2E) as for said first virtual volume (163, 1E), wherein said first virtualization storage device is arranged to transfer an owner right, which is a usage authority to use said logical volume, to said second virtualization storage device so that said owner right is set only to said second virtualization storage device, wherein if said first virtualization storage device receives a first write command from said host computer to said first virtual volume (163, 1E) through said first path after said transfer of said owner right, and does not have said usage authority to use said logical volume which is specified by said owner right, then said first virtualization storage device is arranged to reject processing said first write command thereby causing the host computer to switch from said first path to said second path wherein if said second virtualization storage device has said usage authority to use said logical volume which is specified by said owner right and receives a second write command from said host computer to said second virtual volume (163, 2E) through said second path after said switch, said second virtualization storage device sends a fourth write command corresponding to said second write command to said logical volume. an external storage device including a plurality of physical devices and a controller arranged to set a logical volume on a memory area of said physical devices; a first virtualization storage device including a plurality of first disk devices, and having a first virtual device configured by the plurality of first disk devices and a first virtual volume (163, 1E); and a second virtualization storage device including a plurality of second disk devices, and having a second virtual device configured by the plurality of second disk devices and a second virtual volume (163, 2E); wherein said first virtual volume (163, 1E) is connected to said logical volume, and a first path from a host computer to said first virtual volume (163, 1E) which is accessible by said host computer is defined, wherein said second virtualization storage device is arranged to: acquire information regarding said logical volume in said external storage device from said first virtualization storage device, connect said logical volume, which is detected based on said acquired information, to said second virtual volume (163, 2E) of said second virtualization storage device, and define a second path from said host computer to said second virtual volume (163, 2E) using a same identification number for said second virtual volume (163, 2E) as for said first virtual volume (163, 1E), acquire information regarding said logical volume in said external storage device from said first virtualization storage device, connect said logical volume, which is detected based on said acquired information, to said second virtual volume (163, 2E) of said second virtualization storage device, and define a second path from said host computer to said second virtual volume (163, 2E) using a same identification number for said second virtual volume (163, 2E) as for said first virtual volume (163, 1E), wherein said first virtualization storage device is arranged to transfer an owner right, which is a usage authority to use said logical volume, to said second virtualization storage device so that said owner right is set only to said second virtualization storage device, wherein if said first virtualization storage device receives a first write command from said host computer to said first virtual volume (163, 1E) through said first path after said transfer of said owner right, and does not have said usage authority to use said logical volume which is specified by said owner right, then said first virtualization storage device is arranged to reject processing said first write command thereby causing the host computer to switch from said first path to said second path wherein if said second virtualization storage device has said usage authority to use said logical volume which is specified by said owner right and receives a second write command from said host computer to said second virtual volume (163, 2E) through said second path after said switch, said second virtualization storage device sends a fourth write command corresponding to said second write command to said logical volume.