Can I have more than one undo tablespace in a database?
While you can create more than one undo tablespace in a database, an instance can use only one of them at a time. In a Real Application Clusters environment, you must create at least as many undo tablespaces as the number of instances in the cluster since an undo tablespace can not be shared among instances. For non-RAC databases, there is little reason for having multiple undo tablespaces.