RMAN got ORA-00245 while backing up RAC control file

When backing up control file for RAC databases, you could got ORA-00245 as following,

RMAN> backup device type sbt current controlfile ;

Starting backup at 2016-03-20 19:08:49
allocated channel: ORA_SBT_TAPE_1
channel ORA_SBT_TAPE_1: SID=1941 instance=racdb_1 device type=SBT_TAPE
channel ORA_SBT_TAPE_1: starting full datafile backup set
channel ORA_SBT_TAPE_1: specifying datafile(s) in backup set
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03009: failure of backup command on ORA_SBT_TAPE_1 channel at 03/20/2016 19:08:50
ORA-00245: control file backup failed; in Oracle RAC, target might not be on shared storage

In order to have a consistent version of the control file, RMAN creates a snapshot when asked to back up the control file,
then copy the snapshot control file to backup media.  The default file name of the snapshot is system-dependent, each instance
of same RAC database has default file name,

[oracle@host01 ~]$ export ORACLE_SID=racdb_1
[oracle@host01 ~]$ rman target /

Recovery Manager: Release 11.2.0.3.0 - Production on Thu Mar 21 16:54:07 2016

Copyright (c) 1982, 2011, Oracle and/or its affiliates.  All rights reserved.

connected to target database: racdb (DBID=435209035)

RMAN> SHOW SNAPSHOT CONTROLFILE NAME;

using target database control file instead of recovery catalog
RMAN configuration parameters for database with db_unique_name racdb are:
CONFIGURE SNAPSHOT CONTROLFILE NAME TO '/u01/app/oracle/product/11.2.0/dbhome_1/dbs/snapcf_racdb_1.f'; # default


[oracle@host02]$ export ORACLE_SID=racdb_2
[oracle@host02]$ rman target /

Recovery Manager: Release 11.2.0.3.0 - Production on Thu Mar 21 16:54:07 2016

Copyright (c) 1982, 2011, Oracle and/or its affiliates.  All rights reserved.

connected to target database: racdb (DBID=435209035)

RMAN> SHOW SNAPSHOT CONTROLFILE NAME;

using target database control file instead of recovery catalog
RMAN configuration parameters for database with db_unique_name racdb are:
CONFIGURE SNAPSHOT CONTROLFILE NAME TO '/u01/app/oracle/product/11.2.0/dbhome_1/dbs/snapcf_racdb_2.f'; # default

Depending on whether the RMAN session, which creates snapshot file, is connected to instance racdb_1 running on node host01 or instance racdb_2
running on node host02, the snapshot file name will be snapcf_racdb_1.f or snapcf_racdb_2.f respectively.

When RMAN backs up the control file and the snapshot file is create on other node,  ORA-00245 will be raised up. To avoid the error, the
RMAN Snapshot Control File Location has to be configured on shared storage which is accessible by all nodes in the cluster (all instances of
the RAC databases),

RMAN> CONFIGURE SNAPSHOT CONTROLFILE NAME TO '+FRA/racdb/snapcf_racdb.f';

new RMAN configuration parameters:
CONFIGURE SNAPSHOT CONTROLFILE NAME TO '+FRA/racdb/snapcf_racdb.f';
new RMAN configuration parameters are successfully stored