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 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 each including a memory controller for controlling the input/output processing to/from the nonvolatile semiconductor memories, respectively, the nonvolatile semiconductor memories providing one or more RAID groups,
• the control unit, when updating data stored in one of the nonvolatile semiconductor memories, reads the data to be updated, creates an XOR write command including updated data and the data to be updated, and sends the XOR write command to the memory controller of one of the nonvolatile semiconductor memories where parity data corresponding to the data to be updated is stored by way of the second interface unit, and
• the memory controller, upon receiving the XOR write command, reads out from the one of the nonvolatile semiconductor memories the parity data corresponding to the data to be updated, creates a new parity by carrying out an XOR operation based on the read parity data corresponding to the data to be updated, the updated data and the data to be updated included in the XOR write command, and writes the created new parity to the one of the nonvolatile semiconductor memories.