A method of restoring source data if the source data written in a system region of a hard disk drive and mirror data, which is a copy of the source data, are both damaged, in which the source data is read on a sector basis and error-free sectors and error-generated sectors are determined. The mirror data is read on a sector basis in such a way that sectors corresponding to the error-generated sectors are read. Source data is restored by merging source data read from the error-free sectors and mirror data read from the sectors corresponding to the error-generated sectors.