The database is configured with two control files that must be stored on shared storage.
Every database must have one unique control file. Any additional control files configured for the database are identical copies of the original control file. If a control file becomes unusable, then the database instance fails when it attempts to access the damaged control file. By multiplexing (creating multiple copies of) a control file on different disks, the database can achieve redundancy and thereby avoid a single point of failure.