Patent ID: 8832400

Claim:
A storage system comprising: a storage controller configured to form a virtual volume which is a virtual storage area configured to be a plurality of given size pages, and configured to be a data area and a control information area on the virtual volume, the data area is configured to be a plurality of data parts each of which stores data and the control information area is configured to be a plurality of control information parts each of which stores control information for accessing each of the data parts, respectively; and a storage medium providing the virtual volume with physical storage areas, wherein the storage controller is configured to perform the steps of: expanding the virtual volume on a group basis where the group is a set of the data area and the control information area, where the data area and the control information area each has a given size, respectively; and when receiving a write request for a first data part of the plurality of data parts, allocating a first physical storage area of the physical storage areas to a first page including the first data part if a physical storage area is not already allocated to the first page, and allocating a second physical storage area of the physical storage areas to a second page including a first control information part of the plurality of control information parts if a physical storage area is not already allocated to the second page, where the first control information part stores control information for accessing to the first data part.