RMAN Q & A Page – 2

RMAN INTERVIEW QUESTIONS AND ANSWERS

               Page – 2

11. What is the advantage of  RMAN backup utility ?

RMAN can be  used  in a 24X7  environment  to perform hot backups. But hot backups  were possible  long  before RMAN. So why use RMAN to perform hot backups? There are a couple  of main reasons. If you are not using  RMAN for your hot backups, you have to place table space in backup mode before  you can begin to  make  a backup of that  table space’s data files. When you  place a  tablespace in backup mode, all changes that occur to the tablespace are logged differently in the online redo logs  than  under normal  operating  conditions. This can  cause an increase in the  volume of information written to online redo logs. RMAN does not have this same issue to deal  with  RMAN  performing a hot  backup does not cause  an increase in online redo log volume  during the backup process.

RMAN can also help with incremental backups. The old backup scripts in use  cannot perform incremental backups.

12. How do you see the information about  backups in RMAN?

SQL> Select sid, totalwork, sofar from v$session_longops where sid=153;

13. Can you take image backup using RMAN?

Backup sets, which  are only created and accessed through  RMAN, are  the only from in which RMAN can write backups to media managers such as tape drives and tape libraries  

14. Where RMAN Keeps information of backups, if you are  using  RMAN without catalog?

RMAN  Keeps  information of backups in the control file

15. Do you have to restore data files manually from the backups, if you are doing recovery using RMAN?

Yes

16. A database is running  in ARCHIELOG mode since last one month, A datafile  is added to the  database  last week. Mainly  objects are created in this datafiles. After   one week  this datafile gets damaged before you can take  any backup. Now can you recover his datafile,  you don’t have  any backups?

Yes

17. How does one backup and restore archived log file?

One can backup archived log files using RMAN or any operating system backup utility. Remember to delete files after backing them up to prevent the archive log directory from filling up. If the archive log directory becomes full, your database will hang! Look at this simple RMAN backup scripts

RMAN> run{

2>allocate channel dev1 type disk;

3>backup

4>format '/app/oracle/archback/log_%t_%sp%p'

5>(archivelog all delete input);

6>release channel dev1;

7>}

The "delete input"clause will delete the archived logs as they are blocked-up, List all archivelog backups for the past 24 hours:

RMAN>LIST BACKUP OF ARCHIVELOG FROM TIME 'sysdate-1';

Restore example

RMAN>run{

2>allocate channel dev1 type disk;

3>restore (archive log low logseq 78311 high logseq 78340 thread 1 all);

4>release channel dev1;

5>}

18. Can you take online backup of a control file if yes, how?

SQL> alter database backup control file TO trace As<PATH>

specify the path where you want  to store the control file backup on

19. Where RMAN keeps the information of backup  from backups if you are using RMAN without catalog?

RMAN keeps information of  backups in the  control file

20. Only some blocks are damaged  in a data file, can you just recover doing recovery  using RMAN?

Yes