Archive Logs Enable

11gR2 RAC

1. Set clusetr_database to false for instance:

alter system set cluster_database=false scope=spfile sid='racdb1';

2. Shutdown all instance

srvctl stop database -d racdb

3. Mount Database

startup mount

4. Enable Archiving 

alter database archivelog;

5. Set the parameter cluster_database to true for the instance "racdb1".

alter system set cluster_database=true scope=spfile sid='racdb1';

6. Shutdown the local instance

shutdown

7. Bring up all instance

srvctl start database -d racdb

Once in archive log mode,each instance can archive redo logs automatically;