A test on RMAN new feather--recover.

-bash-3.00$ rman target /

Recovery Manager: Release 10.2.0.2.0 - Production on Thu Apr 9 10:49:21 2009

Copyright (c) 1982, 2005, Oracle. All rights reserved.

connected to target database: ORCL (DBID=1203857279)

RMAN> restore datafile 6;

Starting restore at 09-APR-09
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: sid=154 devtype=DISK

channel ORA_DISK_1: restoring datafile 00006
input datafile copy recid=7 stamp=683715853 filename=/home/oracle/backup/orcl_data_D-ORCL_I-1203857279_TS-TEST_FNO-6_0qkc1b85.bak
destination for restore of datafile 00006: /home/oracle/test01.dbf
ORA-19505: failed to identify file "/home/oracle/backup/orcl_data_D-ORCL_I-1203857279_TS-TEST_FNO-6_0qkc1b85.bak"
ORA-27037: unable to obtain file status
Intel SVR4 UNIX Error: 2: No such file or directory
Additional information: 3
ORA-19600: input file is datafile-copy 7 (/home/oracle/backup/orcl_data_D-ORCL_I-1203857279_TS-TEST_FNO-6_0qkc1b85.bak)
ORA-19601: output file is datafile 6 (/home/oracle/test01.dbf)
failover to previous backup

creating datafile fno=6 name=/home/oracle/test01.dbf
Finished restore at 09-APR-09

From OS side .mv the file to backup directory.
mv orcl_data_D-ORCL_I-1203857279_TS-TEST_FNO-6_0qkc1b85.bak backup

then restore again.

RMAN> recover datafile 6;

Starting recover at 09-APR-09
using channel ORA_DISK_1

starting media recovery

archive log thread 1 sequence 260 is already on disk as file /export/home/workzone/database/oracle/arch/1_260_676076546.dbf
archive log thread 1 sequence 261 is already on disk as file /export/home/workzone/database/oracle/arch/1_261_676076546.dbf
archive log thread 1 sequence 262 is already on disk as file /export/home/workzone/database/oracle/arch/1_262_676076546.dbf
archive log filename=/export/home/workzone/database/oracle/arch/1_260_676076546.dbf thread=1 sequence=260
media recovery complete, elapsed time: 00:00:02
Finished recover at 09-APR-09

RMAN> restore datafile 6;

Starting restore at 09-APR-09
using channel ORA_DISK_1

channel ORA_DISK_1: restoring datafile 00006
input datafile copy recid=7 stamp=683715853 filename=/home/oracle/backup/orcl_data_D-ORCL_I-1203857279_TS-TEST_FNO-6_0qkc1b85.bak
destination for restore of datafile 00006: /home/oracle/test01.dbf
channel ORA_DISK_1: copied datafile copy of datafile 00006
output filename=/home/oracle/test01.dbf recid=8 stamp=683722356
Finished restore at 09-APR-09

RMAN> recover datafile 6;

Starting recover at 09-APR-09
using channel ORA_DISK_1
channel ORA_DISK_1: starting incremental datafile backupset restore
channel ORA_DISK_1: specifying datafile(s) to restore from backup set
destination for restore of datafile 00006: /home/oracle/test01.dbf
channel ORA_DISK_1: reading from backup piece /home/oracle/backup/orcl_0ukc1gpo_1_1.bak
channel ORA_DISK_1: restored backup piece 1
piece handle=/home/oracle/backup/orcl_0ukc1gpo_1_1.bak tag=TAG20090409T103848
channel ORA_DISK_1: restore complete, elapsed time: 00:00:02

starting media recovery
media recovery complete, elapsed time: 00:00:01

Finished recover at 09-APR-09

From SQLPLUS side;
SQL> select file#,status from v$datafile;

FILE# STATUS
---------- -------
1 SYSTEM
2 ONLINE
3 ONLINE
4 ONLINE
5 ONLINE
6 OFFLINE

6 rows selected.

SQL> alter database datafile 6 online;

Database altered.

SQL> select * from v$recover_file;

no rows selected

SQL>conn test/test

SQL> select count(*) from test;

COUNT(*)
----------
3