Patent ID: 8751766

Claim:
A storage system comprising: a plurality of storage devices; a volatile memory which temporarily stores data; a nonvolatile memory; a battery saving power; and a cache control unit which sets, according to battery charging rate of the battery, a part of the data stored in the volatile memory as save target data which are to be saved to the nonvolatile memory when power interruption occurs, and saves the part of the data, which is set as the save target data, to the nonvolatile memory by using power of the battery when power interruption occurs; wherein when the micro processor receives write command from the host computer: the micro processor determines whether sum of the amount of data corresponding to the write command and an amount of dirty data exceeds a first threshold which is determined by the battery charging rate; the microprocessor temporality stores the data corresponding to the write command in the volatile memory as the dirty data if the sum of the amount of data corresponding to the write command and the amount of dirty data does not exceed the first threshold; and the microprocessor stores the data corresponding to the write command in the volatile memory as clean data, and writes the data corresponding to the write command to the plurality of storage devices if the sum of the amount of data corresponding to the write command and the amount of dirty data exceeds the first threshold.