To reduce operational and management costs during normal operations while recovering a database without loss and maintaining on-line performance on a site. A first system includes a primary storage system (103) that stores a DB (107) and a main computer (100) that executes a primary DBMS (101), which provides a DB. A second system includes a secondary (113) that receives from the primary storage system (103) a copy of a log, which shows update differences of the DB (107), and stores a secondary DBMS (117), and a subset (500) that recovers the secondary DB (117) according to the log that is copied from the primary storage system (103). When a failure occurs in the first system, the first system is switched to the second system. A second computer (110) that executes a second DBMS (111) is added to the second system, and the secondary DB (117) that is recovered or is being recovered in the subset (500) is taken over to the second computer (110).