What must you set using the RMAN CONFIGURE command to achieve this?

You configured the default backup device type as disk for RMAN backups. In your database,
because of business requirements, you have to take a simultaneous duplicate backup of the data
files when the RMAN BACKUP command is used.
What must you set using the RMAN CONFIGURE command to achieve this?

A.
MAXSETSIZE TO 2;

B.
DEVICE TYPE DISK PARALLELISM 2;

C.
RETENTION POLICY TO REDUNDANCY 2;

D.
DATAFILE BACKUP COPIES FOR DEVICE TYPE DISK TO 2;

Explanation:
http://docs.oracle.com/cd/B14117_01/server.101/b10734/rcmconc1.htm (Topic backup
redundancy, first paragraph)