A computer system, comprising a server on which an application runs, and a storage system that stores data to be used by the application, the cache driver being configured to change, in a case of the condition of a cache area is a first cache condition in which data is readable from a cache area and writing of data into the cache area is prohibited, the condition of the cache area to a third cache condition in which reading of data from the cache area is prohibited and writing of data into the cache area is prohibited, from the first cache condition.