Disk control device adapted to reduce a number of access to disk devices and method thereof

Abstract

A disk control device is operationally connected to a high-order device and operates a plurality of disk devices. A cache is included in the disk control device for storing data including a plurality of parity data from a corresponding plurality of parity groups in the plurality of disk devices. The disk control device also includes a cache management table for indicating the positions of the data stored in the cache. Cache management means is provided for transferring a selected data request by the host control from the plurality of disk devices to the cache when the cache management table indicates that said selected data is not stored in the cache. Control means transfers the selected data from the cache to the high-order device when the cache management means informs the control means that the selected data is stored in the cache. Moreover, the cache management means holds a selected parity data in the cache when data belonging to the same one of the plurality of parity groups as the selected parity data are stored in the cache, and expels the selected parity data from the cache when no data belonging to the same one of the plurality of parity groups as the selected parity data is stored in the cache.