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October 20, 2012

Oracle RMAN Interview Questions for DBAs

Oracle DBA RMAN Interview Questions/FAQs

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

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

3. Can we use same target database as catalog?
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. How do u know how much RMAN task has been completed?
By querying v$rman_status or v$session_longops

5. From where list and report commands will get input?
Both the commands command quering 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. Command to delete archive logs older than 7days?
RMAN> delete archivelog all completed before sysdate-7;

7. By default how many days backup RMAN stores?

8. What is the use of crosscheck command in RMAN?
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?
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 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?
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 is Level 0, Level 1 backup?
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?
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?

14. What is snapshot control file?
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 backup set and backup piece?
Backup set is logical and backup piece is physical.

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

17. How to do cloning by using RMAN?
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 backup of this (newly created) datafile. How do you restore/recover file?
create the datafile and recover that datafile.
SQL> alter database create datafile ‘…path..’ size n;
RMAN> recover datafile file_id;

19. What is obsolete backup and expired backup?
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 hot backup and RMAN backup?
For hot backup, we have to put database in begin backup mode, then take backup.
RMAN won’t put database in backup mode.

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

22. What are new features in Oracle 11g RMAN?

23. What is the difference between auxiliary channel and maintenance channel?


  1. Please correct the 15 question answer it should be backup set is logical and backup piece is physical

  2. Hi Satya,

    You're posts are really very help full to me i need a help from you. Could you please post some more real time interview questions for RMAN,ASM and RAC.


  3. Hi Seshu,

    Thank you very much...
    All these interview questions are real time. I faced all these questions (each question at least 3 times).

    Oracle RMAN Interview Questions/FAQs

    Oracle ASM Interview Questions/FAQs

    Oracle RAC Interview Questions

    All the best.

    -Cheers, Satya

    1. Hi Satya,

      Really thanks a lot for your help.


  4. Sir Really i have no words to describe regarding your Website .
    Its Really Helpful and really short and sweet.

    Once again thanks for creating this blog.

  5. Good blog. Thanks for providing info about RMAN, RAC

  6. Hi Satya,

    First time I read your blog all docs are very useful .. kindly share some tuning releated

  7. Hi Satya,

    Plse correct question 10 as Differential backup (for level 1 parents only) and Cumulative backup (for level 0 or level 1 parents)


  8. Hi Satya, Always ur post helpful and learned a lots from here. Hope this may also useful:
    Oracle RMAN Interview Questions and Answers