What is RMAN? How to take database backup using RMAN?
RMAN:
Recovery Manager is a tool
that manages the process of creating backup and also manages the process of
restoring and recovering them during disaster situations. In addition to RMAN
repository records, the recovery catalog can also hold RMAN stored scripts,
sequences of RMAN commands for common backup tasks. With RMAN we can be 100%
sure that our database has been backed up. Moreover we can take check whether
the backup files are valid or not. Further we can take incremental backups
which results in improvement of performance during backup and recovery time.
Backup process can be made faster using Parallel operation. In RMAN backup
method no Extra redo generated when backup is taken compared to online backup.
With the compression algorithm facility in RMAN we can save space in hard disk.
RMAN Maintains repository of backup metadata. RMAN related views store backup
locations.RMAN helps us in identifying the files which need to be backed up.
Before taking RMAN backup it
is mandatory that the database should be in Archive log mode. Check whether it
is enabled or not
SQL>
archive log list
Database log
mode
Archive Mode
Automatic
archival
Enabled
Archive
destination
/u01/oracle/app/oradata/pavan/ttdtest/flash_recovery_area/TTDTEST/archivelog
Oldest online log
sequence 20
Next log sequence to
archive 22
Current log
sequence 22
Let’s see start taking
backup with RMAN
rmantarget /
RMAN
>BACKUP DATABASE;
RMAN
>exit;
The above process is a simple
way of taking database backup using RMAN. We are not sure where the backup is
taken/what is it's size/what is the format of it? Generally the backup location
is either flash recovery area or $ORACLE_HOME/dbs location by default.
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RMAN BACKUP SCRIPT:
The below script is a simple,
efficient, compressed algorithm used one. We will learn all RMAN related tags
and their purpose with in short time.
RMAN>
run{
CONFIGURE RETENTION POLICY TO
RECOVERY WINDOW OF 14 DAYS;
CROSSCHECK ARCHIVELOG ALL;
CROSSCHECK BACKUP;
allocate channel t1 type disk format
'/u01/ttdtest/flash_recovery_area/TTDTEST/backupset/ORA_rman_full_backup_ttdtest_%U.bck'
maxpiecesize 5120m;
backup incremental level = 0 AS
COMPRESSED BACKUPSET database tag = full_open_backup_disk;
release channel t1;
allocate channel t3 type disk format
'/u01/ttdtest/flash_recovery_area/TTDTEST/backupset/ORA_rman_arch_backup_ttdtest_%U.bck';
backup archivelog until time
'sysdate -1' delete input;
sql
'alter system archive log current';
backup archivelog all;
backup current controlfile format
'/u01/ttdtest/flash_recovery_area/TTDTEST/backupset/ORA_rman_ctrl_backup_ttdtest_%U.bck';
delete noprompt obsolete;
delete noprompt expired backup;
delete noprompt expired archivelog
all;
release channel t3;
}
Exit
Now i can see all my files in
u01/ttdtest/flash_recovery_area/TTDTEST/backupset/
location.
v$rman_status is the view that maintains all RMAN backup related information.
RMAN
Commands:
We can return any setting to
its default value by using CONFIGURE command or
we can change the settings .
RETENTION POLICY
TO RECOVERY WINDOW OF 14 DAYS
-----> indicates that we are will be keeping our database backup file for
next 14 days. After that it will become obsolete/invalid which is no longer
useful for restore and recovery.
CROSSCHECK
ARCHIVELOG ALL
-----> indicates that it is checking the archive logs whether
they are valid or not
CROSSCHECK BACKUP -----> tells us whether the
previously taken database backups are valid or not/Check whether backup items
still exist
allocate
channel ----->
this command is to manually assign a channel to back up specified files. An
RMAN channel represents one stream of data to a device type.
Type disk ----->indicates backup files are
going to take in disk
Format ----->indicates the naming
convention of my backup files and their extention with .bck format. it can be
any
maxpiecesize 5120m----->indicates that my each backup
file should be atmost 5GB of size.
Backup incremental
level = 0 ----->indicates
that i am taking full backup of database. other than this i can iake
incremental,cumulative database backups as per my wish just by replacing 0 with
either 1 or 2.
COMPRESSED ----->indicates that the backup
should be compressed one.the purpose of using this is it will reduce the backup
size.
Tag =
full_open_backup_disk
----->A tag is a symbolic name for a backup set. it tells us that it is full
backup.
release channel t1
----->RELEASE
CHANNEL command to release a normal or maintenance channel while maintaining a connection
to a target database instance.
Allocate channel
t3 & release channel t3 ----->channel
t3 is initiated and closed for backing up archive logs
backup archivelog
until time 'sysdate -1' delete input
----->indicates that it is taking backup of archive logs till before 24
hours and dekleting the files from disk
sql 'alter
system archive log current'
----->this indicates a normal sql to take a log switch. the purpose of it is
to archive all transactions
backup archivelog
all ----->it backs up
all the archivelogs till now
backup current
controlfile
----->indicates taking backup of control file
delete noprompt
obsolete
----->indicates deletion of previous backups(greater than 14 days) without
prompting/asking
delete noprompt
expired backup ----->indicates
deletion of expired(manually deleted in OS level) backups without
prompting/asking
delete noprompt
expired archivelog all ----->indicates
deletion of expired archivelogs without prompting/asking.
in RMAN prompt type
show all , then it will display all the settings defined for rman.
The backup we took from above
steps are useful for recovery operations in future(with in 14 days).
Happy learning....!!!
