A storage system carries out database reorganization processing. In a method of reorganizing, a database which is stored in a disk drive of a storage device is reorganized. The disk drive contains a first volume where the database is stored and a second volume paired with the first volume to store a copy of the database. The reorganization method includes the steps of: making transactions from the host computer into a quiescent state; splitting the paired first volume and second volume so as to only allow the database in the first volume to be accessed; releasing the quiescent state of the transactions; reorganizing the second volume; and copying data in the second volume to the first volume to resynchronize and pair the first volume and the second volume with each other.