The present invention provides a method including a step of determining whether a number of storage media usable for one of input and output of processing data is not smaller than one plus a number of storage media necessary for one of input and output of processing data when a request for reconstruction of stored data is detected, a step of identifying storage media to be operated of the usable storage media when a positive result is obtained, a step of specifying one of the storage media to be operated as a storage medium for reconstruction and the other storage media as storage media for one of the input and output of the processing data, and shifting specification of the storage medium for reconstruction in each command cycle, and a step of performing one of the input and output of the processing data and reading of a processing unit for reconstruction in parallel with each other in accordance with the specification of the storage media, and reconstructing the stored data and recording the reconstructed stored data on a storage medium as a reconstruction destination in a stage in which all of processing units necessary to reconstruct the stored data are prepared.