Storage subsystem

A storage subsystem, comprising:

• a first interface unit for sending and receiving information to and from a host computer via a network;
• a storage apparatus for storing data;
• a second interface unit, which is connected to the storage apparatus, and which carries out data input/output processing to/from the storage apparatus;
• a control unit for controlling via the second interface unit the input/output processing to/from a plurality of logical devices allocated to a storage areas of the storage apparatus;
• and
• a cache memory for temporarily storing data in accordance with the processing of the control unit as a control target for the control unit,
• wherein
• the storage apparatus comprises a plurality of nonvolatile semiconductor memories;
• and a memory controller for controlling the input/output processing to/from the nonvolatile semiconductor memories,
• the control unit creates an XOR write command for carrying out an XOR write to a parity-storage nonvolatile semiconductor memory from among the nonvolatile semiconductor memories, and transfers the created XOR write command to the memory controller by way of the second interface unit, and
• the memory controller, upon receiving the XOR write command, reads out from the parity-storage nonvolatile semiconductor memory an old parity specified by the XOR write command, creates a new parity by carrying out an exclusive OR operation based on the read-out old parity and a plurality of data attached to the XOR write command, and write the created new parity to the parity-storage nonvolatile semiconductor memory.