Provided is a storage system capable of saving actually used physical storage areas and of achieving a high speed in write processing. There is disclosed a computer system including a server and a storage system, in which physical storage areas of a disk drive are managed for each one or more physical blocks of predetermined sizes, and allocation of one or more physical blocks to a plurality of logical blocks of predetermined sizes is managed, and the storage system stores data written in a first logical block in a first physical block allocated to the first logical block and allocates the first physical block to a second logical block where the same data as the data stored in the first physical block is to be written.