Disclosed is a system and method for reducing an overhead of storing a log of each host processor in a cluster system that includes a plurality of host processors. Part of a disk cache of a disk system shared by the plurality of host processors is used as a log storage area. In order to make this possible, the disk system is provided with an interface enabled to be referred to and updated from each of the host processors separately from an ordinary I/O interface. A storage processor controls an area of the disk cache used for ordinary I/O processes by means of a disk cache control table. And a storage processor controls a log area allocated in the disk cache by means of an exported segments control table. The disk cache area registered in the exported segments control table is mapped into the virtual address space of the main processor by an I/O processor.