The invention is to efficiently exchange storage programs. A storage program in an active state and a storage program in a standby state in a storage program group each change metadata thereof when the storage program in the active state writes data. When update of the storage programs including arranging post-update storage programs in storage nodes and generating new-version metadata based on old-version metadata by the post-update storage programs is to be performed, the post-update storage program in the standby state generates the new-version metadata based on the old-version metadata is performed for the storage programs in the plurality of storage nodes while replacing the active state and the standby state of the storage programs with each other in the plurality of storage programs in the storage program group.