How to backup and restore the Oracle Control File

There are two approaches to take Backup of control file in Oracle:

• Backing it up in a binary format


• Backing it up in a human readable format

Syntax: 
alter database backup controlfile to ['filename' | trace]

This command comes in two versions. One backs up the control file in a binary format while the other backs it up in a human readable form. It is required if the database is running in archive log mode and a structural change was made to the database.

Backing it up in a binary format:

You can generate a binary image of the Control File

SQL Code: 
alter database backup controlfile
               to '/some/arbitrary/path';
alter database backup controlfile
               to '/some/arbitrary/path' reuse;

Backing it up in a human readable format:

You generate a text file script which will re-generate a Control File when run as a SQL script. The file name will be something like 'ora_<some numbers>.trc'

SQL Code:
alter database backup controlfile to trace;

Check udump directory for text based controlfile.

Syntax:
alter database backup controlfile to trace
               as '/some/arbitrary/path';
alter database backup controlfile to trace
               as '/some/arbitrary/path' reuse;

If the human readable form is chosen, the file can be made usable if the comments at the beginning are removed and replaced with a connect / as sysdba. If the init.ora file is not at its default location, it has to be appended with a pfile=.... in the line containing a startup.

Restore the control file

The trouble starts when you attempt to restore the binary version of the Control File backup. Because it was an exact, binary copy of a Control File, its SCN number will not agree with the SCN in the headers of all the data files -basically, the Master Clock is out of whack. You therefore have to issue the following command

RECOVER DATABASE USING BACKUP CONTROLFILE;

It tells the system not to pay too much attention to the SCN of the Control File. Unfortunately, after you issue that command (and following any recovery that it might cause to take place), you must open the database with the following command:

ALTER DATABASE OPEN RESETLOGS;

You can also use RMAN script to restore and recover control file to all locations specified in the parameter file then restore the database, using that control file:

SQL Code
STARTUP NOMOUNT;
RUN
{
  ALLOCATE CHANNEL c1 DEVICE TYPE sbt;
  RESTORE CONTROLFILE;
  ALTER DATABASE MOUNT;
  RESTORE DATABASE;
}

Restore control file to default location:

The default location is defined by CONTROL_FILES parameter of pfile/spfile. If you don't specify any location while restoring your control file then the control file will be restored to the location set by CONTROL_FILES parameter.

RMAN Code: 
RMAN> SET DBID 7887865467
RMAN> RUN {
      RESTORE CONTROLFILE FROM AUTOBACKUP;
     }

Restore of the Control File from Control File Autobackup

For the use who are using  recovery catalog, you can restore your control file from an autobackup. The database must be in a NOMOUNT state. And you have to set DBID. RMAN uses the autobackup format and DBID to determine where to find for the control file autobackup.

RMAN Code:
RMAN> SET DBID 7887865467
RMAN> RUN {
        SET CONTROLFILE AUTOBACKUP FORMAT
        FOR DEVICE TYPE DISK TO 'autobackup_format';
        RESTORE CONTROLFILE FROM AUTOBACKUP;
      }

Restoring a Control File When Using a Recovery Catalog

The recovery catalog contains a complete record of the backups of Database, including backups of the control file. Therefore, It is not necessary to mention the DBID or control file autobackup format.

RMAN Code:
$rman TARGET / CATALOG cpdb/cpdb
RMAN> RESTORE CONTROLFILE;

Restore of the Control File From a Known Location

If you know the backuppiece of controlfile or any copy then simply you can use,

RMAN Code: 
RMAN> RESTORE CONTROLFILE from 'filename';

Restore of the Control File to a New Location

In prior cases RMAN restore the control file to the location specified by CONTROL_FILES parameter of the spfile or pfile.If you want to restore the control file to another location use,

RMAN Code:
RMAN> RESTORE CONTROLFILE TO '<new_location>';

It is also possible to change CONTROL_FILES parameter and then perform RESTORE CONTROLFILE to change location.

Limitations When Using a Backup Control File

After Complete the restore and recover the control file  using a backup control file, It is mandatory  run RECOVER DATABASE and perform an OPEN RESETLOGS on the database. Where SCN is change.