Interfaces of SAN and NAS, prevents data miss even when a trouble occurs and makes it possible that an arbitrary number of NAS interfaces access the same file system with high performance. A storage system includes multiple interfaces for external connection, multiple disks accessed from multiple interfaces, and a shared memory accessed from multiple interfaces. The multiple interfaces are block interfaces executing disk block I/O request, and file interfaces of file servers executing file I/O request. A file system in the file servers is constructed in a part of the disks, and a log storage area holding change log of the file system, and a management file server information storage area holding information of managing file server performing exclusive access control of file system and management of log storage area are formed in the shared memory.