In a computer system in which a server has, in addition to a disk used for booting, an operation transfer destination disk that has the same content as the boot disk, a method for changing the disk used by the server or another server in the computer system for booting to the operation transfer destination disk is realized by changing the content of the operation transfer destination disk to enable the OS and applications installed in the operation transfer destination disk to be booted from the destination disk and by changing the setting of a boot program of the server to enable booting from the operation transfer destination disk.