Patent ID: 7757042

Claim:
A control method in a storage system, said storage system including: a controller coupled to a host computer and controlling to read/write data sent from said host computer to at least one storage region, a plurality of disk drives corresponding to said storage region, said disk drives being used as a RAID group and storing data sent from said host computer and parity data created based on data sent from said host computer, at least one spare disk drive being used to read/write in a new RAID group with a remainder of disk drives other than a first disk drive, the control method comprising: a first step, when said first disk drive whose error occurrence count exceeds a threshold, for reading data from said remainder of disk drives, and creating data based on said read data, and writing said created data to said spare disk drive, and a second step for judging whether failure has occurred in a first sector in at least one of said remainder of disk drives during said first step, and, in a case that failure has occurred in said first sector in at least one of said remainder of disk drives, attempting to read data from a second sector in said first disk drive, said second sector corresponding to said first sector, a third step for judging whether said data can be read from said second sector in said first disk drive, and, in a case that data can be read from said second sector in said first disk drive, writing said read data from said second sector in said first drive to said spare disk drive, and, in a case that data cannot be read from said second sector in said first disk drive, data in said second sector in said first disk drive is treated as data lost.