October 1, 2023

30 Top Oracle RMAN basic/advanced Interview Questions for DBAs

Frequently asked Oracle DBA RMAN (Recovery Manager) Real-time Interview Questions


0. What is RMAN and why to use RMAN?
Answer :

1. Difference between catalog and nocatalog?
Answer :
Recovery catalog is central and can have information from many databases.

2. Difference between using the recovery catalog and the control file in Oracle?
Answer :
When a new incarnation happens, the old backup information in the control file will be lost. It will be preserved in the recovery catalog.
In the recovery catalog, we can store scripts.
Recovery catalog is central and can have information from many databases.

3. Can we use the same target database as catalog?
Answer :
No. The recovery catalog should not reside in the target database (database to be backed up), because the database can't be recovered in the mounted state.

4. As DBA, how do you know the progress of the Oracle RMAN task?
Answer :
By querying v$rman_status or v$session_longops

5. From where list and report commands will get input?
Answer :
Both the commands command querying v$ and recovery catalog (RC) views. V$BACKUP_FILES or many of the recovery catalog views such as RC_DATAFILE_COPY or RC_ARCHIVED_LOG.

6. What is the command to delete archive logs older than 7days?
Answer :
RMAN> delete archivelog all completed before sysdate-7;

7. By default how many days backup RMAN stores in Oracle Database?
Answer :

8. What is the use of crosscheck command in RMAN?
Answer :
Crosscheck will be useful to check whether the catalog information is intact with OS-level information.

9. What are the differences between crosscheck and validate commands?
Answer :
Validate command is to examine a backup set and report whether it can be restored. RMAN scans all of the backup pieces in the specified backup sets and looks at the checksum to verify that the contents are intact so that the backup can be successfully restored if necessary.

Crosscheck command is to verify the status of backups and copies recorded in the RMAN repository against media such as disk or tape. The crosscheck command only processes files created on the same device type as the channel running crosscheck.

10. Which is one is good, differential (incremental) backup or cumulative (incremental) backup?
Answer :
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.

11. What are Level 0, Level 1 backups in Oracle?
Answer :
A level 0 incremental backup, which is the base for subsequent incremental backups, copies all blocks containing data, backing the datafile up into a backup set just as a full backup would. A level 1 incremental backup can be either of the following types:
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.

12. Can we perform level 1 backup without level 0 backup?
Answer :
If no level 0 backup is available, then the behavior depends upon the compatibility mode setting.
If compatibility < 10.0.0, RMAN generates a level 0 backup of the file contents at the time of the backup.
If compatibility is >= 10.0.0, RMAN copies all blocks changed since the file was created, and stores the results as a level 1 backup. In other words, the SCN at the time the incremental backup is taken is the file creation SCN.

13. Will RMAN put the database/tablespace/datafile in backup mode?
Answer :
Nope.

14. What is a snapshot control file in Oracle?
Answer :
The snapshot control file is a copy of a database control file created in an operating system-specific location by RMAN. RMAN creates the snapshot control file so that it has a consistent version of a control file to use when either resynchronizing the recovery catalog or backing up the control file.

15. What is the difference between a backup set and a backup piece?
Answer :
Backup set is logical and backup piece is physical.

16. RMAN command to backup for creating standby database?
Answer :
RMAN> duplicate target database to standby database ....

17. How to do cloning by using Oracle RMAN?
Answer :
RMAN> duplicate target database …

18. Suppose you lost one datafile and DB is running in ARCHIVELOG mode. You have full database backup of 1 week/day old and don’t have a backup of the (newly created) datafile. How do you restore/recover file?
Answer :
Create the datafile and recover that datafile.
SQL> alter database create datafile '…path...' size n;
RMAN> recover datafile file_id;


19. What is an obsolete backup and expired backup?
Answer :
A status of "expired" means that the backup piece or backup set is not found in the backup destination.
A status of "obsolete" means the backup piece is still available, but it is no longer needed. The backup piece is no longer needed since RMAN has been configured to no longer need this piece after so many days have elapsed, or so many backups have been performed.

20. What is the difference between a hot backup and RMAN backup?
Answer :
For hot backup, we have to put the database in begin backup mode, then take backup.
RMAN won’t put the database in backup mode.

21. How to put manual/user-managed backup in RMAN (recovery catalog)?
Answer :
By using catalog command.
RMAN> CATALOG START WITH '/tmp/backup.ctl';

22. What were the new features in Oracle 11g RMAN?
Answer :

23. What were the new features in Oracle 12c RMAN?
Answer :

24. What is the difference between the auxiliary channel and the maintenance channel?
Answer :

25. What is the use of nofilenamecheck in RMAN ?
Answer :
When NOFILENAMECHECK is used with the DUPLICATE command, RMAN does not validate the filenames during restoration. If the primary database and the standby database are on the same host, The DUPLICATE NOFILENAMECHECK option should not be used.

26. Do we need to shutdown the database to change the block change tracking file?
Answer :
No need

27. How will you identify a Physical Corruption/Logical corruption?
Answer :

28. What happens if you lose SPFILE and PFILE and DB crashed with some error, how will you start the database?
Answer :

29. What are the database file's that RMAN cannot backup ?
Answer :
RMAN cannot take backup of the pfile, redo logs, TNS or network configuration files, password files, external tables and the contents of the Oracle home files.

30. Can I take RMAN backup when the database is down ?
Answer :
No, we can take RMAN backup only when the target database is open or in the mount stage.

31. How to check RMAN configuration ?
Answer :

32. Can we have archive logs and datafile backup in a single backupset ?
Answer : No

33. Can we take RMAN backup when the target database is down ?
Answer : No

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