A compact data processing system suitable for long-term use that enables the maintenance of failure resistance without having to mount many spare disks or replace disks; a data processing method; and a storage apparatus for this data processing system are provided. In the data processing system, which has a host system and a storage apparatus that provides first memory areas for storing data read/written by the host system, the storage apparatus has a reservation unit that dynamically reserves one of the first memory areas as a spare second memory area when a failure occurs in any one of the first memory areas and there is no spare second memory area to migrate the data stored in that faulty memory area to.