Abstract: A higher reliable storage array system. A plurality of data storage devices store data; a spare storage device replaces one of the plurality of data storage devices; and a control unit controls an I/O operation of the plurality of data storage devices and the spare storage device. The control unit includes means for storing a history of self recovered errors of each one of the plurality of data storage devices, means for calculating an error rate of each of the plurality of data storage devices on the basis of the history of errors, means for judging a necessity to execute a preventive maintenance of each one of the plurality of data storage devices from the error rate, and means for executing the preventive maintenance.

Abstract: A battery module comprises at least one battery, and one or more memory sections for memorizing management information of the at least one battery at cutting operation of connection, when a connection between the at least one battery and at least one external device is cut, and the at least one battery and the memory sections are structured as one body.