Saturday, February 7, 2009

oracle: rman feature

let us first check the disadvantages of user managed backups:

i) you have to manually keep track of your backup files location, their status and whether they are available while restoring
ii) you can not perform incremental backups using user managed backup strategies. everytime you need to take full backup
iii) you have to manually take backup of various oracle files (copy and paste or through operating system utility)
iv) restore of database also require manual interaction.You may need to write operating system script to do the task of backup and restore operations.
v) You need to put your datafiles in backup mode if you are taking backup of database while it is online for user operations . These may end up becoming major performance issue .
vi) You need to restore the datafiles may be archive files also manually while restore your database.

as of ORACLE , user managed backup is a way to take backup of your database . But oracle refers rman tool to be used for its enhanced feature .
The practical way of implementation is make your main backup strategy with rman tool while user-managed backup should be your second backup plan

Check the rman features following:
i) it automatically manages the backup files with some default configuration in place . we can configure these default options . So as a dba ,no need to remember and maintain the backup files location
ii) rman interface supports simple backup and recovery commands to perform the task
iii) rman provides report of every backup operations which is very helpful
iv) it will delete the old/unnecessary backups with the default configuration in place. we can change this default settings as our requirement.
v) you can verify/test that whether your backups are healthy to be restored , without actually restoring the data.
vi) we can perform incremental backups .
vii) while taking backups , it can detect block corruption of your datafiles which will be logged in v$database_block_corruption view.
ix) we can take image copies of our database (same as copy/paste in user managed backups)
x) if only some blocks are corrupted in your datafile , rman can restore only that blocks instead of restoring the complete datafile.
xi) rman does not take backup of unused blocks of your daatfiles( unlike user managed backup)
xii) you can configure rman to use third party storage like tape drives.
xiii) we can write scripts with easy commands to run the scripts automatically on a scheduled time
xiv) we can take encrypted backups
xv) rman supports compression features
xvi) rman supports active duplication to perform database duplications
xvii) rman has data recovery advisor features to diagnose and repair data failures and corruptions
xvii) rman has rman catalog feature , to store rman metadata forever , so that you have alternate location to store rman information and scripts . rman catalog can store for multiple databases rman metadata together
xix) You can query v$rman_output and v$rman_status to get the status of your current running rman commands and status of the job
sql> select sid,recid,stamp,output from v$rman_output;

---------- ---------- ---------- ---------------------------------------------------------------------------
146 1 678195976 connected to target database: LION (DBID=396604920)
146 2 678195976
146 3 678195982
146 4 678195982 Starting backup at 07-FEB-09
146 5 678195983 using target database control file instead of recovery catalog
146 6 678195983 allocated channel: ORA_DISK_1
146 7 678195983 channel ORA_DISK_1: sid=144 devtype=DISK
146 8 678195984 channel ORA_DISK_1: starting full datafile backupset
146 9 678195984 channel ORA_DISK_1: specifying datafile(s) in backupset
146 10 678195984 input datafile fno=00001 name=D:\LION\DATA\SYSTEM.DBF
146 11 678195984 channel ORA_DISK_1: starting piece 1 at 07-FEB-09

11 rows selected.

to know more about rman .......

thanks ,
have a nice day........................................

Knowing is not enough; we must apply.
Willing is not enough; we must do.

Johann Wolfgang von Goethe

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