Storage apparatus and control method thereof

A storage system comprising:

• a plurality of storage devices, and
• a storage controller configured to manage a plurality of pages in a pool provided by at least one of the plurality of storage devices, to provide a virtual storage area to a host by allocating one or more pages from the pool dynamically, in which the virtual storage area is formed with a data area and a control information area,
• wherein the storage controller is configured to expand the virtual storage area on a unit basis, where the unit is a set of a given size area of the data area and a given size area of the control information area,
• wherein, in response to a write request from the host, the storage controller is configured to store data into the data area and to store control information for accessing to the data into the control information area, and
• wherein, in response to a read request from the host, the storage controller is configured to read data from the data area by using the control information stored in the control information area.