A storage system according to the present invention has a plurality of flash packages equipped with a deduplication function. When a storage controller transmits a write data and a feature value of write data to a flash package, the flash package compares contents of the write data with data having a same feature value as the feature value of the write data. As a result of the comparison, if there is no corresponding data, the write data is stored in the flash memory, but if there is a corresponding data, the new data will not be stored. Thus, a greater number of data can be stored in the flash memory while preventing deterioration of performance.