RMAN> configure channel device type disk format '/oracle/orclarch/%U_%d';

new RMAN configuration parameters:
CONFIGURE CHANNEL DEVICE TYPE DISK FORMAT   '/oracle/orclarch/%U_%d';
new RMAN configuration parameters are successfully stored

RMAN> backup tablespace users;

Starting backup at 30-JUN-10
allocated channel: ORA_DISK_1
channel ORA_DISK_1: sid=136 devtype=DISK
channel ORA_DISK_1: starting full datafile backupset
channel ORA_DISK_1: specifying datafile(s) in backupset
input datafile fno=00004 name=/oracle/oradata/orcl/users01.dbf
channel ORA_DISK_1: starting piece 1 at 30-JUN-10
channel ORA_DISK_1: finished piece 1 at 30-JUN-10
piece handle=/oracle/orclarch/03lhh2ja_1_1_ORCL tag=TAG20100630T085922 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:01
Finished backup at 30-JUN-10

RMAN> exit