Patent ID: 8458400

Claim:
A storage apparatus comprising: a storage control device which contains a cache memory, the cache memory having a plurality of cache segments; a plurality of storage drive devices connected to the storage control device; a storage pool volume provided by the storage drive devices, the storage pool volume being divided into a plurality of pages; and a logical unit (LU) provided to a host computer to which one of the plurality of pages is assigned from the storage pool volume, the LU being a target to be resident in the cache memory, wherein the storage control device is configured to have an LU management table for managing information of the LU, wherein the storage control device is configured to have a cache segment management table which includes a plurality of records, for each of the cache segments and having addresses of data stored in each respective cache segment, the addresses identifying a location of the data in the assigned page, wherein, in response to receipt of a request from the host computer for creating the LU, the storage control device is configured to add an ID and a size of the LU to the LU management table, and wherein, in response to receipt of an IO request, to the LU from the host computer, which addresses an area where a page has not been assigned, the storage control device is configured to assign the assigned page to the LU from the storage pool volume, reserve one or more of the cache segments with the same size as the assigned page without assigning the reserved cache segments to any other LU, and add one or more of the records corresponding to the reserved cache segments.