Patent ID: 7640407

Claim:
A method of migrating data in a computer system including a computer and a plurality of storage systems, the computer including an interface, a processor, and a memory, each of the plurality of storage systems including an interface, a processor, and a memory, the plurality of storage systems including a first storage system, a second storage system, and a third storage system, the method comprising: a first step of coupling the first storage system to the computer and the second storage system, the first storage system having a first storage area for storing data written by the computer; a second step of coupling the second storage system to the first storage system and the third storage system, the second storage system having a second storage area for storing data; a third step of coupling the third storage system to the computer and the second storage system, the third storage system having a virtual storage area corresponding to the second storage area; a fourth step of migrating data stored in the first storage area to the second storage area; a fifth step of converting an access request to the virtual storage area into an access request to the second storage area and issuing the converted access request to the second storage system; and a sixth step of migrating the data migrated to the second storage area to a third storage area created in the third storage system based on a determination result between a value of the data migrated to the second storage area and a predetermined threshold value.