Provided is a storage system and power supply control method thereof, storage apparatus and data processing method capable of reducing the power consumption of the overall storage system without requiring any complicated settings. A journal regarding update history information of a first volume in which a host system reads and writes data is created. The created journal is sequentially stored in a second volume or a first external storage apparatus, each of which serves as a storage destination of the journal. Power supply of a storage device providing an alternate second volume as the storage destination of the journal or an alternate first external storage apparatus as the storage destination of the journal is controlled according to the storage quantity of the journal in the second volume or the first external storage apparatus.