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ORACLE RMAN BACKUP
This article shows how to setup and configure RMAN backups.
A. ENABLING ARCHIVELOG MODE
When you enable ARCHIVELOG Mode, you will prevent REDO logs to be overwritten.
To enable archiving let’s first check the current archiving mode:
SQL> SELECT LOG_MODE FROM SYS.V$DATABASE;
LOG_MODE
------------
NOARCHIVELOG
After ensuring that we are on NOARCHIVELOG mode, we can enable archiving:
SQL> startup mount
ORACLE instance started.
Total System Global Area 184549376 bytes
Fixed Size 1300928 bytes
Variable Size 157820480 bytes
Database Buffers 25165824 bytes
Redo Buffers 262144 bytes
Database mounted.
SQL> alter database archivelog;
Database altered.
SQL> alter database open;
Database altered.
After opening database, let’s check if we were successful:
B. SCHEDULING RMAN BACKUP
a. RMAN SCHEDULING VIA ORACLE ENTERPRISE MANAGER (OEM)
In order to schedule RMAN backup via oracle enterprise manager, you need to
login to OEM successfully with your SYS account. After loging in, navigate to
“Maintenance-> Schedule Backup".
To perform successful backup, you need to inform Oracle about your operating
system login credentials because Oracle will need to access database files
through your os file security system.
ATTENTION: When you change your operating system password, do not
forget to update your OS credentials info on OEM previously scheduled RMAN jobs.
Later on, choose “customized backup” to specify your backup strategy and choose
“whole database” as the object you want to backup unless you have another
specific purpose. Now you will see the page which will allow you to save all the
details you want your RMAN backup schedule has.
Lets explore these properties in details one by one:
Backup Type: There are two types of backups strategizes you can choose
which are full backups and incremental backups. We will go in more details on
incremental backups because it has a amazing algorithm inside.
- Full Backups
- Incremental Backups: RMAN incremental backups back up only datafile
blocks that have changed since a specified previous backup. You can make
incremental backups of databases, individual tablespaces or datafiles. The goal
of an incremental backup is to back up only those data blocks that have changed
since a previous backup.
Incremental Backup Algorithm: Each data block in a datafile contains a
system change number (SCN), which is the SCN at which the most recent change was
made to the block. During an incremental backup, RMAN reads the SCN of each data
block in the input file and compares it to the checkpoint SCN of the parent
incremental backup. If the SCN in the input data block is greater than or equal
to the checkpoint SCN of the parent, then RMAN copies the block. Note that if
you enable the block change tracking feature, RMAN can refer to the change
tracking file to identify changed blocks in datafiles without scanning the full
contents of the datafile. Once enabled, block change tracking does not alter how
you take or use incremental backups, other than offering increased performance.
Incremental backups either be Level 0 (same as full back up) or Level 1 (details
are below).
Differential or Cumulative Level1 Incremental Backups:
• A differential backup, which backs up all blocks changed after the most
recent incremental backup at level 1 or 0.
• A cumulative backup, which backs up all blocks changed after the most recent
incremental backup at level 0.
Incremental backups are differential by default.
HINT: Cumulative backups are preferable to differential backups when
recovery time is more important than disk space, because during recovery each
differential backup must be applied in succession. Use cumulative incremental
backups instead of differential, if enough disk space is available to store
cumulative incremental backups.
• Backup Mode: If your database is in ARCHIVELOG mode, you can take
ONLINE backups which means you can have your in OPEN mode during backup. On the
other hand, if your database is in NOARCHIVELOG mode, when your backup job
starts it will shutdown your database and start up your database in mount state.
After finishing backup procedure, your backup job will alter your database to
open state.
• Advanced: If you mark “Also backup all archived logs on disk” option,
rman will backup your achived logs. If you also mark “Delete all archived logs
from disk after successfully backing up” rman will delete them after backing up.
This option is useful when you start to have disk size problems. Marking “Use
Proxy copy supported by media management software to perform a backup” will let
you enable RMAN turns over control of the data transfer to a media manager that
supports this feature. When you mark “Delete obsolete backups” option, the
retention policy determines which backups and image copies are obsolete. If
selected, the obsolete backups and copies will be deleted when the backup is
finished.
When you click NEXT button, you will see a screen which will ask you about where
would you like to store your backup files, you can either choose disk backup or
tape backup:
Third step is setting the job schedule:
Later on, fourth step is checking the RMAN script and submitting the job:
b. RMAN SCHEDULING VIA RMAN SCRIPTING
If you no longer have a particular archivelog file you can let RMAN catalog
know this by issuing the following command at the rman prompt after
connecting to the rman catalog and the target database -
change archivelog all crosscheck ;
C. RESTORING/RECOVERING FROM RMAN BACKUP
a. Connecting to RMAN
After connecting to RMAN command prompt, we can set retention policy to recovery
window, redundancy and controlfile autobackup on options as below:
SOURCE
1. Enabling ARCHIVELOG Mode, http://www.cuddletech.com/articles/oracle/node58.html
2. Oracle® Database Backup and Recovery Basics, http://download-uk.oracle.com/docs/cd/B19306_01/backup.102/b14192/bkup004.htm
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