Storage system and storage control method

A storage system comprising:

• a non-volatile storage device;
• a storage controller configured to process data to be read and written from and to the storage device using a storage function;
• and
• a volatile memory,
• wherein the storage controller is configured to, when receiving a data write request,
• store data related to the received data write request in the memory,
• create a log related to the data stored in the memory and store the log in the memory,
• store the log, which is stored in the memory, in the storage device,
• execute a completion response to a source of the data write request after the log is stored in the storage device, and
• process the data stored in the memory using the storage function and destage the data in the storage device,
• wherein when the log is stored in the storage device, the log in the memory related to the log in the storage device is invalidated, and
• wherein when the data is destaged, the log in the storage device related to the destaged data is invalidated.