Patent ID: 8924663

Claim:
A storage system, comprising: a first auxiliary storage device for storing storage target data; a second auxiliary storage device having a higher data reading/writing speed than a data reading/writing speed of the first auxiliary storage device; a main storage device having a higher data reading/writing speed than the data reading/writing speeds of the first auxiliary storage device and the second auxiliary storage device; a CPU (Central Processing Unit): wherein the CPU stores storage target data in the first auxiliary storage device, manages a storing position of the storage target data using feature data which is based on a data content of the storage target data, manages data, by referring to the feature data from index data which is based on a data content of the feature data; determines, by using the feature data based on a data content of storage target data to be newly stored and the index data based on the data content of the feature data, whether or not storage target data which is identical to the storage target data to be newly stored has already been stored in the first auxiliary storage device, and when managing the storage target data, stores and keeps, in the main storage device, the index data based on the feature data by referring to the feature data of the storage target data stored in the first auxiliary storage device, and if the index data stored and kept in the main storage device reaches a preset amount, stores and keeps, in the second auxiliary storage device, the index data stored and kept in the main storage device, and deletes the index data stored and kept in the second auxiliary storage device from the main storage device, and combines a plurality of units of the index data stored and kept in the second auxiliary storage device and the index data stored and kept in the main storage device and again stores the combined data in the second auxiliary storage device, and deletes the index data before being combined from second auxiliary storage device and the main storage device.