Patent ID: 6976124

Claim:
A disk array device connected to an external device, comprising a plurality of disk devices and a control device controlling the disk devices, said control device comprising: request receiving means for receiving a request from said external device; formatting means for performing a format process to said disk device according to said received request; read means for performing a data reading process in response to said received request; write means for performing a data writing process in response to said received request; a write history management table for recording a history of said performed writing process to said disk device in block units; and a cache memory for temporarily storing data; wherein said formatting means refers to said write history management table, confirms whether or not said writing process has been performed with regard to blocks to be formatted, performs said format process only to said blocks on which writing processes have not been performed, and records a history of completing said writing process of said formatted blocks in said write history management table, and in a state of performing said formatting means, if said request receiving means receives a request said to perform reading process and/or writing process from said external device, said read means and/or write means refers to said write history management table, and only when writing processes have been performed on the block to be written to, accesses said disk array device to perform said reading process and/or said writing process to said block; and wherein in a state of performing said formatting process, if said request receiving means receives a request from said external device to perform said reading process, said read means refers to said write history management table, and if said writing processes have not been performed on a block to be read, then said read means creates predetermined data, said predetermined data is stored in said cache memory, and said data from said cache memory is sent to said external device.