Oracle 11gR2 RAC Enable Archive log Mode.

In the cluster log in from anyone of the instances.

In my case it is DELL1

[oracle@rac1 ~]$ export ORACLE_SID=dell1
[oracle@rac1 ~]$ sqlplus / as sysdba

SQL*Plus: Release 11.2.0.1.0 Production on Thu Oct 4 16:38:15 2012

Copyright (c) 1982, 2009, Oracle.  All rights reserved.


Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
With the Partitioning, Real Application Clusters, Automatic Storage Management, OLAP,
Data Mining and Real Application Testing options

# Remove this instance from the cluster.

SQL> alter system set cluster_database=false scope=spfile sid='dell1';

System altered.


# Stop the whole database.

[oracle@rac1 ~]$ srvctl stop database -d dell


# Start this instance in mount mode and enable archive log mode.

[oracle@rac1 ~]$ sqlplus / as sysdba

SQL*Plus: Release 11.2.0.1.0 Production on Thu Oct 4 16:41:08 2012

Copyright (c) 1982, 2009, Oracle.  All rights reserved.

Connected to an idle instance.

SQL> startup mount
ORACLE instance started.

Total System Global Area  535662592 bytes
Fixed Size                  1337720 bytes
Variable Size             390071944 bytes
Database Buffers          138412032 bytes
Redo Buffers                5840896 bytes
Database mounted.



SQL> alter database archivelog;

Database altered.

SQL> alter system set cluster_database=true scope=spfile sid='dell1';

System altered.

SQL> shutdown immediate
ORA-01109: database not open


Database dismounted.
ORACLE instance shut down.

# Start the whole database.

[oracle@rac1 ~]$ srvctl start database -d dell


[oracle@rac1 ~]$ sqlplus / as sysdba

SQL*Plus: Release 11.2.0.1.0 Production on Thu Oct 4 16:44:49 2012

Copyright (c) 1982, 2009, Oracle.  All rights reserved.


Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
With the Partitioning, Real Application Clusters, Automatic Storage Management, OLAP,
Data Mining and Real Application Testing options

SQL> archive log list;
Database log mode              Archive Mode
Automatic archival             Enabled
Archive destination            USE_DB_RECOVERY_FILE_DEST
Oldest online log sequence     1
Next log sequence to archive   2
Current log sequence           2