The data processing system controls, from the database management system on a host computer, the storage device subsystem which stores log data supplied from the database management system; allocates on a disk cache in the storage device subsystem in advance a log-dedicated buffer area of a size equal to that of the log data output between checkpoints; writes log data into the buffer area; and, in the event of a host computer failure, reads out the log data from the disk cache without making access to a disk device. Since the log information required for the recovery of the data processing device is cached on the storage device side, the time it takes to read the necessary log information can be shortened, which in turn reduces the system recovery time.