It is provided a storage system for storing write data requested by a host computer, comprising: a data storage device, first and second cache memories, first and second non-volatile memories and at least one power storage device, wherein the storage system stores the requested write data in the data storage device, without storing the requested write data in neither the first cache memory nor the second cache memory in a case where the amount of charge of the at least one power storage device is smaller than the predetermined amount of power, and stores the requested write data in at least one of the first and second cache memories, and then store the requested write data in the data storage device in a case where the amount of charge of the at least one power storage device is equal to or larger than the predetermined amount of power.