According to the prior art storage system, in order to add a storage device to a pool after a storage system has been operated for a certain period of time, the performance may be varied significantly according to the access performance of the application using the pool, and it was not possible to realize an optimum allocation corresponding to the operation form if the storage device is set to be included in a pool of a given tier based on the type of the storage device. Therefore, the present invention provides a system in which a performance test is performed in accordance with an access tendency of the application using the pool to thereby compute the tier capable of having the storage device added thereto, based on which the storage device can be allocated to an appropriate pool.