[oracle@localhost oradata]$ rman target /

Recovery Manager: Release 10.2.0.3.0 - Production on Mon Jun 27 05:50:03 2011

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

connected to target database: TASM (DBID=3032096031)

RMAN> sql ‘alter tablespace xff offline’;

using target database control file instead of recovery catalog

sql statement: alter tablespace xff offline

RMAN> backup device type disk as copy datafile 6 format '+DG2';

Starting backup at 27-JUN-11

using target database control file instead of recovery catalog

allocated channel: ORA_DISK_1

channel ORA_DISK_1: sid=159 devtype=DISK

channel ORA_DISK_1: starting datafile copy

input datafile fno=00006 name=+DATA/tasm/xff01.dbf

output filename=+DG2/tasm/datafile/xff.256.754899605 tag=TAG20110627T062003 recid=4 stamp=754899608

channel ORA_DISK_1: datafile copy complete, elapsed time: 00:00:07

Finished backup at 27-JUN-11

RMAN> switch tablepspace xff  to copy;

datafile 6 switched to datafile copy "+DG2/tasm/datafile/xff.256.754899605"

RMAN> sql 'alter tablespace xff online';

sql statement: alter tablespace xff online

SQL> select name from v$datafile;

NAME

--------------------------------------------------------------------------------

+DATA/tasm/system01.dbf

+DATA/tasm/undotbs01.dbf

+DATA/tasm/sysaux01.dbf

+DATA/tasm/users01.dbf

+DATA/tasm/example01.dbf

+DG2/tasm/datafile/xff.256.754899605

6 rows selected.

SQL> select count(*) from hr.a;

  COUNT(*)

----------

      1580