Storage system and method for controlling storage system

A storage system comprising:

• a storage device that stores data;
• a control unit that performs input/output processing on the data for the storage device according to a request from a host computer;
• a volatile memory that temporarily keeps the data and keeps a cache directory which shows a storage location for the data by entry;
• a non-volatile memory that includes a volatile cache save area and a cache directory save area;
• and
• a battery that electrically powers the volatile memory during an electric power interruption when electric power supply to the volatile memory is interrupted,
• wherein the control unit saves the cache directory from the volatile memory to the cache directory save area and saves the data from the volatile memory to the volatile cache save area during the electric power interruption, and copies the cache directory from the cache directory save area to the volatile memory, changes the storage location of the data in the cache directory whose storage location prior to the saving is the volatile memory to the volatile cache save area, and initiates host I/O processing when the electric power supply is resumed,
• wherein the cache directory also stores whether or not the data is stored in the storage device by entry, and
• wherein the control unit copies the cache directory to the non-volatile memory, copies the data whose storage location prior to the saving is the volatile memory and which is not stored in the storage device from the non-volatile memory to the volatile memory, changes the storage location of the copied data in the cache directory to the copy location, and initiates the host I/O processing when the electric power supply is resumed.

A method for controlling a storage system including a storage device that stores data, a control unit that performs input/output processing on the data for the storage device according to a request from a host computer, a volatile memory that temporarily keeps the data and keeps a cache directory which shows a storage location for the data by entry, a non-volatile memory that includes a volatile cache save area and a cache directory save area, and a battery that electrically powers the volatile memory during an electric power interruption when electric power supply to the volatile memory is interrupted, the method comprising:

• a step for saving the cache directory from the volatile memory to the cache directory save area and saving the data from the volatile memory to the volatile cache save area during the electric power interruption, and copying the cache directory from the cache directory save area to the volatile memory, changing the storage location of the data in the cache directory whose storage location prior to the saving is the volatile memory to the volatile cache save area, and initiating host I/O processing when the electric power supply is resumed,
• wherein the cache directory also stores whether or not the data is stored in the storage device by entry, and
• wherein the cache directory is copied to the non-volatile memory, the data whose storage location prior to the saving is the volatile memory and which is not stored in the storage device is copied from the non-volatile memory to the volatile memory, the storage location of the copied data in the cache directory is changed to the copy location, and the host I/O processing is initiated when the electric power supply is resumed.