A storage system have a plurality of control modules which control a plurality of disk storage devices. In order to read/write system information even when problems arise in paths with the plurality of disk devices, and moreover to output log data even upon occurrence of an abnormality in the control module, a plurality of control modules which control a plurality of disk storage devices, each have a built-in system disk device unit which stores log data. In equalization processing, log data of one control module is stored in a system disk of another installed control module. Even when an abnormality occurs in the one control module, log data of the one control module can be output by the other control module.