Storage system

A storage system comprising:

• a storage device;
• and
• a storage controller configured to receive data from a host computer and to store the received data in the storage device,
• wherein the storage controller comprises:
• a processor;
• a volatile first cache memory that is coupled to the processor and that temporarily stores the data;
• a nonvolatile second cache memory that is coupled to a microprocessor and that temporarily stores the data;
• and a battery that is configured to supply electrical power to at least the processor and the first cache memory when a power stoppage has occurred,
• wherein the second cache memory comprises a dirty data area for storing dirty data, which is data that is not stored in the storage device, and a remaining area other than the dirty data area, and
• the processor, when a power stoppage has occurred, is configured to store as target data, in the remaining area of the second cache memory, either all or a part of the data stored in the first cache memory.