Patent ID: 7376804

Claim:
A storage system comprising: a first storage unit for storing information from a first server; a second storage unit for storing the information stored in said first storage unit; and a storage controller being coupled with said first storage unit, said second storage unit, said first server, and a second server, and being used to control said first storage unit and said second storage unit, wherein when an instruction for splitting is received from said first server, said storage controller reports end of the splitting to said first server, receives an instruction for backup from said second server, and then transfers information to a backup device from said second storage unit after copy of information from said first storage unit to said second storage unit ends, wherein a state of differential data is checked, wherein if the differential data exist representing that backup data is not reflected in the second storage unit, then data within a range to be backed up is fully read and transferred to the second storage unit and then transferred to a tape device serving as the backup device, and wherein if the differential data does not exist representing that all data within the range to be backed up is reflected in the second storage unit, then the data is read from the second storage unit and transferred to the tape device.