Take the backup datafiles which are not backed up?

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Take the backup datafiles which are not backed up?
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$rman

Recovery Manager: Release 11.2.0.1.0 - Production on Mon 30 DEC 21:23:22 2013

Copyright (c) 1982, 2009, Oracle and/or its affiliates.  All rights reserved.

RMAN> connect target /;

connected to target database: PROD (DBID=246965557)

RMAN> BACKUP DATABASE NOT BACKED UP;

Starting backup at 30-DEC-13
using channel ORA_DISK_1
skipping datafile 1; already backed up on 30-DEC-13
skipping datafile 2; already backed up on 30-DEC-13
skipping datafile 3; already backed up on 30-DEC-13
skipping datafile 4; already backed up on 30-DEC-13
Finished backup at 30-DEC-13

RMAN>

let me add a datafile to the tablespace
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SQL> select file_name from dba_data_files;

FILE_NAME
--------------------------------------------------------------------------------
/d01/oracle/oradata/prod/users01.dbf
/d01/oracle/oradata/prod/undotbs01.dbf
/d01/oracle/oradata/prod/sysaux01.dbf
/d01/oracle/oradata/prod/system01.dbf

SQL> alter tablespace users add datafile '/d01/oracle/oradata/prod/users02.dbf' size 200m;

Tablespace altered.

SQL>


RMAN> BACKUP DATABASE NOT BACKED UP;

Starting backup at 30-DEC-13
using channel ORA_DISK_1
skipping datafile 1; already backed up on 30-DEC-13
skipping datafile 2; already backed up on 30-DEC-13
skipping datafile 3; already backed up on 30-DEC-13
skipping datafile 4; already backed up on 30-DEC-13
channel ORA_DISK_1: starting full datafile backup set
channel ORA_DISK_1: specifying datafile(s) in backup set
input datafile file number=00005 name=/d01/oracle/oradata/prod/users02.dbf
channel ORA_DISK_1: starting piece 1 at 30-DEC-13
channel ORA_DISK_1: finished piece 1 at 30-DEC-13
piece handle=/d01/oracle/flash_recovery_area/PROD/backupset/2013_12_30/o1_mf_nnndf_TAG20131230T200659_9d318d1j_.bkp tag=TAG20131230T200659 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:01
Finished backup at 30-DEC-13

Starting Control File and SPFILE Autobackup at 30-DEC-13
piece handle=/d01/oracle/product/11.2.0/dbs/cfc-246965557-20131230-04 comment=NONE
Finished Control File and SPFILE Autobackup at 30-DEC-13

RMAN>