A storage system have a plurality of control modules which control a plurality of disk storage devices, in which system information reading/writing is possible even when problems arise in paths with a plurality of disk devices, and moreover log data can be output even upon occurrence of an abnormality in a control module. A plurality of control modules has built-in a pair of system disk device units which store log data. Upon occurrence of an abnormality in one control module, a system disk unit of one control module is removed and mounted in another control module, and the log data of the mounted system disk unit is output by the another control module.