Enable Flashback in oracle RAC database

bash-4.3$ srvctl stop database -d dcdbrac
bash-4.3$ sqlplus "/as sysdba"

SQL*Plus: Release 11.2.0.4.0 Production on Tue Nov 22 00:52:44 2016

Copyright (c) 1982, 2013, Oracle.  All rights reserved.

Connected to an idle instance.

SQL> startup mount;
ORACLE instance started.

Total System Global Area 6.3069E+10 bytes
Fixed Size                  2393728 bytes
Variable Size            9059699072 bytes
Database Buffers         5.3989E+10 bytes
Redo Buffers               18116608 bytes
Database mounted.
SQL> alter database flashback on;

Database altered.

SQL> show parameter DB_FLASHBACK_RETENTION_TARGET

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
db_flashback_retention_target        integer     1440
SQL> alter database open;

Database altered.

SQL> select flashback_on  from v$database;

FLASHBACK_ON
------------------
YES

SQL> exit
Disconnected from Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, Real Application Clusters, Automatic Storage Management, Oracle Label Security,
OLAP, Data Mining, Oracle Database Vault and Real Application Testing options
bash-4.3$
bash-4.3$ srvctl stop instance -d dcdbrac -i dcdbrac1
bash-4.3$ srvctl start database -d dcdbrac
bash-4.3$