环境：
DB VERSION: 11.2.0.4.0
RAC 2 nodes

问题：
邮件显示rman备份失败，查看rman备份日志

Starting Control File and SPFILE Autobackup at 2013-12-30 04:07:02
released channel: c1
released channel: c2
released channel: c3
released channel: c4
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03009: failure of Control File and SPFILE Autobackup command on c1 channel at 12/30/2013 04:07:05
ORA-00245: control file backup failed; target is likely on a local file system <---------

控制文件自动备份失败。大概意思是控制文件的备份不应该放在本地文件系统上。

解决办法：

在rac一个节点的rman中，修改SNAPSHOT CONTROLFILE NAME参数指定到ASM共享存储位置。
注意：在一个节点的rman中修改，会自动将改变同步到其他节点的rman中。

CONFIGURE SNAPSHOT CONTROLFILE NAME TO '+data1/xxxx/snapcf_xxx.f';

===========================================================================
以下根据metalink的相关文档整理
ORA-245: In RAC environment from 11.2 onwards Backup Or Snapshot controlfile needs to be in shared location (文档 ID 1472171.1)

错误原因：
Oracle Database - Enterprise Edition - Version 11.2.0.1.0 and later
Information in this document applies to any platform.
This issue is only applicable to RAC database.
该问题会出现在11.2.0.1.0及之后的RAC环境中。

From 11gR2 onwards, the controlfile backup happens without holding the controlfile enqueue. For non-RAC database, this doesn't change anything. But for RAC database, due to the changes made to the controlfile backup mechanism in 11gR2, any instance in the cluster may write to the snapshot controlfile. Due to this snapshot controlfile need to be visible to all instances.

11gR2之后，备份控制文件无需锁定controlfile enqueue。在非Rac中，没有任何改变。但是，在rac环境中，由于11gR2的控制文件备份原理发生了变化，集群中的每个实例都要能够写到快照控制文件。所以，快照控制文件要对所有实例可见。

The snapshot controlfile MUST be accessible by all nodes of a RAC database, if the snapshot controlfile does not reside on a shared device error will be raised at the time of RMAN backup while taking snapshot of controlfile. 
在Rac中，所有节点都必须能够访问快照控制文件。如果快照控制文件没有放到共享设备上，当rman备份快照控制文件时，ORA-00245错误就会出现。

This applies to backing up controlfile using sqlplus / having autobackup of controlfile configured on nonshared location.
???

ORA-245 error message description
----------------------------------------
00245, 00000, "control file backup operation failed"
*Cause: Failed to create a control file backup because some process
signaled an error during backup creation.
*Action: Check alert files for further information. This usually happens
because some process could not access the backup file during
backup creation. Any process of any instance that starts a
read/write control file transaction must have an access to the
backup control file during backup creation.

下面操作都会引起ORA-245错误
1. In RAC environment controlfile autobackup fails with ora-0245

Autobackup of controlfile in RMAN is failing with error:
RMAN-571: ===========================================================
RMAN-569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-571: ===========================================================
RMAN-3009: failure of Control File and SPFILE Autobackup command on 
ORA_DISK_1 channel at 10/27/2010 12:13:31
ORA-245: control file backup operation failed

2. In RAC environment, backup controlfile to non shared location fails

SQL> ALTER DATABASE BACKUP CONTROLFILE TO '/home/rac1122/test/control.bk' REUSE
*
ERROR at line 1:
ORA-245: control file backup operation failed

3. In RAC environment backing up standby controlfile to non shared location fails
SQL> alter database create standby controlfile as '/home/oracle/renostdbycntrl.ctl';

alter database create standby controlfile as 
'/home/oracle/renostdbycntrl.ctl'
*
ERROR at line 1:
ORA-245: control file backup operation failed

4. In RAC environment copy current controlfile to '${DB_BACKUP_DIR}/rac_tnctv_control.bak';
channel ch1: starting datafile copy
copying current control file
RMAN-571: ===========================================================
RMAN-569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-571: ===========================================================
RMAN-3009: failure of backup command on 10/07/2011 11:36:42 channel at ch1
ORA-245: control file backup operation failed

5. In RAC environment, Rman backup fails if snapshot controlfile is not in shared location.

RMAN-00571: ========================================================
RMAN-00569: ============ ERROR MESSAGE STACK FOLLOWS =============
RMAN-00571: =========================================================
RMAN-03009: failure of resync command on default channel at 03/13/2012 10:19:41
ORA-00245: control file backup operation failed

解决办法：
This is a RAC specific 'configuration' issue and the correct configuration is as described below

It is changed behaviour which requires that the snapshot controlfile in a RAC environment, is on a shared location. 
1. Check the snapshot controlfile location:
RMAN> show snapshot controlfile name;

2. Configure the snapshot controlfile to a shared disk:
RMAN> CONFIGURE SNAPSHOT CONTROLFILE NAME TO '<shared_disk>/snapcf_<DBNAME>.f';

Or in case of ASM use
RMAN> CONFIGURE SNAPSHOT CONTROLFILE NAME TO '+<DiskGroup>/snapcf_<DBNAME>.f';