If Oracle Database allows multiple instances to mount the same database concurrently, then the CLUSTER_DATABASE initialization parameter setting can make the database available to multiple instances. Database behavior depends on the setting:
- If CLUSTER_DATABASE is false (default) for the first instance that mounts a database, then only this instance can mount the database.
- If CLUSTER_DATABASE is true for the first instance, then other instances can mount the database if their CLUSTER_DATABASE parameter settings are set to true. The number of instances that can mount the database is subject to a predetermined maximum specified when creating the database
其中：其中rac架构11g之前cluster_database=false，才能改归档模式；11g之后在修改归档模式时已经不需要设置此参数。
