Enable and Disable Archivelog mode in 11G.

****Enable Archive Log Mode***

Please find the below steps required to enable archive log mode on an 11g database.

Verify the database log mode.

[oracle@ngqa ~]$ sqldba

SQL*Plus: Release 11.2.0.3.0 Production on Mon Jan 27 19:01:01 2014

Copyright (c) 1982, 2011, Oracle.  All rights reserved.

Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

SQL>  archive log list
Database log mode              No Archive Mode
Automatic archival             Disabled
Archive destination            USE_DB_RECOVERY_FILE_DEST
Oldest online log sequence     25
Current log sequence           27
SQL>
The log mode is No Archive Mode. Note that Archive destination is USE_DB_RECOVERY_FILE_DEST. You can determine the path by looking at the parameter RECOVERY_FILE_DEST.

SQL> show parameter recovery_file_dest

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
db_recovery_file_dest                string      /orabin/ora11gR2/flash_recovery
                                                 _area
db_recovery_file_dest_size           big integer 3852M
SQL>
By default, archive logs will be written to the flash recovery area. If you do not want to write archive logs to the flash recovery area you can set the parameter LOG_ARCHIVE_DEST_n to the location in which you wish to write archive logs.

SQL> alter system set log_archive_dest_1='LOCATION=/oradata/oraarch/MMINDQA/' scope = both;

System altered.

SQL> archive log list;
Database log mode              No Archive Mode
Automatic archival             Disabled
Archive destination            /oradata/oraarch/MMINDQA/
Oldest online log sequence     25
Current log sequence           27
SQL>
SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount
ORACLE instance started.

Total System Global Area  849530880 bytes
Fixed Size                  1339824 bytes
Variable Size             511708752 bytes
Database Buffers          331350016 bytes
Redo Buffers                5132288 bytes
Database mounted.
SQL>
Lastly all that is needed it set archive log mode and open the database.

SQL> alter database archivelog;

Database altered.

SQL> alter database open;

Database altered.

SQL> archive log list
Database log mode              Archive Mode
Automatic archival             Enabled
Archive destination            /oradata/oraarch/MMINDQA/
Oldest online log sequence     25
Next log sequence to archive   27
Current log sequence           27
SQL>
We can now see that archive log mode is enabled. Notice that Automatic archive is enabled as well.

You can switch to the log file to see that an archive is written to archive log location.

SQL> alter system switch logfile;

System altered.

SQL> host

[oracle@ngqa ~]$ ls /orabin/oraarch/arch
1_27_711369564.dbf
[oracle@ngqa ~]$ exit
exit
SQL>

***Disable Archive Log Mode***

Note: It is recommended to perform a backup of the database (after a shutdown normal or immediate) prior to changing the archive status of a database.

The following are the steps required to disable archive log mode on an Oracle 10g or 11g database.

Verify the database log mode.
[oracle@ngqa ~]$ sqldba

SQL*Plus: Release 11.2.0.3.0 Production on Mon Jan 27 19:01:01 2014

Copyright (c) 1982, 2011, Oracle.  All rights reserved.

Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

SQL>  archive log list;
Database log mode              Archive Mode
Automatic archival             Enabled
Archive destination            /oradata/oraarch/MMINDQA/
Oldest online log sequence     26
Next log sequence to archive   28
Current log sequence           28
SQL>
The Database log mode is Archive mode. Next we shut down the database and bring up back up in mount mode.

SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount
ORACLE instance started.

Total System Global Area  849530880 bytes
Fixed Size                  1339824 bytes
Variable Size             511708752 bytes
Database Buffers          331350016 bytes
Redo Buffers                5132288 bytes
Database mounted.
SQL>
All that is left is to disable archive log mode and open the database.

SQL> alter database noarchivelog;

Database altered.

SQL> alter database open;

Database altered.

SQL> archive log list;
Database log mode              No Archive Mode
Automatic archival             Disabled
Archive destination            /oradata/oraarch/MMINDQA/
Oldest online log sequence     26
Current log sequence           28
SQL>
As you can see, ARCHIVELOG mode has been disabled.