When data is used by a write-enabled process and a write-disabled process for a secondary storage device, latest system configuration data such as a patch can be used by both processes in real time, while data which should not be shared between both processes can be isolated and used. A mirror volume B of a volume A (an actual volume on the secondary storage device) is created when a PC is started, and the write-disabled process is caused to read from and write to only the volume A, and the write-enabled process is caused to read from and write to only the mirror volume B. The system configuration data such as an OS patch is written to both the volume A and the mirror volume B so that the latest system configuration data can be handled from both the write-disabled process and the write-enabled process. At this time, a section which redirects all write processes for the volume A and the mirror volume B onto a memory is used to cache all the write processes for the volume A and the mirror volume B, on the memory, and only the cache of the mirror volume B is written to the secondary storage device at a time of shutdown.