Patent ID: 8806163

Claim:
A storage system to be connected to a host and another storage system for back up, comprising: a first storage unit; a second storage unit including updated data storage areas; and a controller configured to receive a write request for updated data from the host for transmission of the updated data to the first storage unit, the controller executing a process including determining, when receiving the write request for the updated data, whether there is a free area having capacity enough to store the updated data in a storage area to be processed that is one of the updated data storage areas, wherein when determining that there is the free area, storing control information into the second storage unit, the control information including first writing destination information indicating a writing area of the updated data within the first storage unit, second writing destination information indicating a writing area of the updated data within the another storage system for backup and identification information of one of the updated data storage areas used as the storage area to be processed, and writing the updated data into the first storage unit, and wherein when determining that there is not the free area, changing the storage area to be processed to another one of the updated data storage areas within the second storage unit, storing the control information into the second storage unit, writing the updated data into the first storage unit, and instructing change of a storage area to be processed to another storage system to be connected to the host, reading out the updated data that is written in the first storage unit to each of the updated data storage areas of the second storage unit in accordance with the control information stored in the second storage unit in asynchronous with processing of the write request from the host, and transmitting the updated data on the updated data storage areas that is read out and the second writing destination information relating to the updated data to the another storage system for backup.