Wednesday, March 23, 2011

Control File Autobackups

One of the many features included in rman is the ability to automatically backup your control file. What is a control file? The control file contains information about your database including its physical structure. If you are using rman without a recovery catalog then your backup information is also stored in the control file.

It is very important for (some) recovery purposes to ensure you have a recent copy of your control file, especially if it contains your recovery catalog. There is one feature of control file autobackups which alot of dba's seem to be unfamiliar with, which is why I thought i'd write up a brief article on it. If you have this feature enabled and you make a structural change to the database, the control file is automatically backed up. ie, If you add a datafile, rename a file, etc. Information which could affect your ability to recover. This backup will be placed on disk even if your regular backup goes to tape.

A quick test. First, ensure you have control file autobackups enabled and select a location on disk. By default the control file backup will be placed in your $ORACLE_HOME/dbs directory unless you specify a location.

oravis@myserver=> rman target / nocatalog

Recovery Manager: Release 10.2.0.2.0 - Production on Wed Jan 16 14:48:49 2008

Copyright (c) 1982, 2005, Oracle. All rights reserved.

connected to target database: VIS (DBID=767668735)
using target database control file instead of recovery catalog

RMAN> CONFIGURE CONTROLFILE AUTOBACKUP ON;

new RMAN configuration parameters:
CONFIGURE CONTROLFILE AUTOBACKUP ON;
new RMAN configuration parameters are successfully stored

RMAN> CONFIGURE CONTROLFILE AUTOBACKUP FORMAT FOR DEVICE TYPE DISK TO '/oradata/bck/vis_backup/%F';

new RMAN configuration parameters:
CONFIGURE CONTROLFILE AUTOBACKUP FORMAT FOR DEVICE TYPE DISK TO '/oradata/bck/vis_backup/%F';y


A quick test to make sure the backup works and is on disk:


oravis@myserver=> rman target / nocatalog

Recovery Manager: Release 10.2.0.2.0 - Production on Wed Jan 16 15:25:24 2008

Copyright (c) 1982, 2005, Oracle. All rights reserved.

connected to target database: VIS (DBID=767668735)
using target database control file instead of recovery catalog

RMAN> backup current controlfile;

Starting backup at 16-JAN-08
allocated channel: ORA_DISK_1
channel ORA_DISK_1: sid=414 devtype=DISK
channel ORA_DISK_1: starting full datafile backupset
channel ORA_DISK_1: specifying datafile(s) in backupset
including current control file in backupset
channel ORA_DISK_1: starting piece 1 at 16-JAN-08
channel ORA_DISK_1: finished piece 1 at 16-JAN-08
piece handle=/mnt1/app/visdb/1020_64bit/dbs/01j6adrd_1_1 tag=TAG20080116T152532 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:02
Finished backup at 16-JAN-08

Starting Control File Autobackup at 16-JAN-08
piece handle=/oradata/bck/vis_backup/c-767668735-20080116-00 comment=NONE
Finished Control File Autobackup at 16-JAN-08

RMAN> exit

Recovery Manager complete.
oravis@myserver=> ls -alrt /oradata/bck/vis_backup
total 42036
drwxrwxr-x 28 oravis dba 1024 Jan 16 14:47 ..
-rw-rw---- 1 oravis dba 19398656 Jan 16 15:25 c-767668735-20080116-00
drwxrwxr-x 2 oravis dba 512 Jan 16 15:25 .


Next we need to make a structural change to the database to see if the control file is automatically backed up. For this example i'll add a small datafile to the system tablespace.


SQL> alter tablespace SYSTEM add datafile '/oradata/dbf/visdata/system09.dbf' size 25M;

Tablespace altered.


A directory listing of the backup location should show a second control file backup:


oravis@myserver=> ls -alrt /oradata/bck/vis_backup
total 79972
drwxrwxr-x 28 oravis dba 1024 Jan 16 14:47 ..
-rw-rw---- 1 oravis dba 19398656 Jan 16 15:25 c-767668735-20080116-00
-rw-rw---- 1 oravis dba 19398656 Jan 16 15:26 c-767668735-20080116-01
drwxrwxr-x 2 oravis dba 512 Jan 16 15:26 .




Regards,
Sukhwinder Singh

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