A storage system 1 including multiple slots for loading a block I/O interface controller, a file I/O interface controller, and any other kinds of interface controllers that are combined freely. The storage system 1 includes a management table that manages fail-over-enabled devices by grouping those devices in accordance with the interface type and the domain to which each device belongs; an information table that directs a fail-over procedure; and fail-over controlling means that takes over the processing of a failed interface controller belonging to a fail-over-enabled group. The fail-over system offers several modalities for monitoring failures, selecting takeover controllers and restoring functionality. Storage system 1 solves conventional problems by providing a system that can mount a plurality of file systems, and that resists multiple failures detected in a fail-over server.