Patent ID: 7320055

Claim:
A storage system comprising: a cache control unit for managing data, which is in a cache memory, in a page data unit including a plurality pieces of block data each of which serving as an access unit of an upper system, and processing an input or output request of the upper system with respect to a storage device; and a write-back process unit for reading out a first discontinuous area from the storage device, subjecting it to a merge so as to generate a merged continuous area, and performing a write back, in a case in which dirty data in the cache memory which has been updated by the upper system and is newer than stored data in the storage device is to be written back to the storage device, and when the first discontinuous area is determined in a page of the dirty data; wherein, when, as a distribution of dirty data in a page, at least one third continuous area is present between a first continuous area nearest the page head and a second continuous area nearest the page end via discontinuous areas, the write-back process unit determines a second discontinuous area including the third continuous area between the first continuous area and the second continuous area, reads it out from the storage device, generates the merged continuous area by subjecting the read out data of the area which is present in the second discontinuous area and other than the third continuous area to a merge, and performs a write back.