The storage system is coupled to a computer and includes a plurality of physical storages being used to configure a first logical storage and a second logical storage, a control unit receiving a read request and a write request from the computer; and a cache memory storing data which is sent to the computer. The control unit determines whether a request from the computer is a write request or a read request. If it is a read request, the control unit reads data from the cache memory or at least one of the plurality of physical storages based on the read request. If it is a write request, the control unit determines whether destination of the write request is the first logical storage.