RMAN Q & A Page – 5

RMAN INTERVIEW QUESTIONS AND ANSWERS

                                                                     

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41.  What is the difference between restoring and recovering?

Restoring involves copying backup files from secondary storage (backup media) to disk. This can be done to replace damaged files or to copy/move a database to a new location. 
Recovery is the process of applying redo logs to the database to roll it forward. One can roll-forward until a specific point-in-time (before the disaster occurred), or roll-forward until the last transaction recorded in the log files. 

SQL> connect SYS as SYSDBA

SQL> RECOVER DATABASE UNTIL TIME '2001-03-06:16:00:00' USING BACKUP CONTROLFILE;

42. What are the common RMAN errors?

Some of the common RMAN errors are: 
RMAN-20242: Specification does not match any archivelog in the recovery catalog.
Add to RMAN script: sql alter system archive log current';
RMAN-06089: archived log xyz not found or out of sync with catalog
Execute from RMAN: change archive log all validate

43. Which RMAN command is used to create an exact replica of a database in new host?

Duplicate database

44. List  some of the RMAN catalog view names which contain the catalog  information?

RC_DATABASE_INCARNATION

RC_BACKUP_COPY_DETAILS

RC_BACKUP_CORRUPTION

RC_BACKUP_DATAFILE_SUMMARY to name a few

45. Is there any encryption  option available in the RMAN?

RMAN offers 3  encryption  mode

Dual mode

Password mode  and

Transparent mode

46. How to identified the corrupted  block in RMAN? How to fix it?

By using v$database_block_corruption;

V$database_block_corruption and dba_extents to identify

Corrupt blocks and  associated objects

Oracle corruption is most frequently caused by a bad disk, although there are rare cases of "logical" corruption within the Oracle data blocks. Oracle also provides a v$database_block_corruption view that you can check:

select * from v$database_block_corruption

If you know the file number and block number you can run the following query to see the exact data block that has corruption:

select     relative_fno,     owner,     segment_name,    segment_type
from    dba_extents where     file_id = 6 and
437 between block_id and block_id + blocks - 1;

Once you know the exact block ID you can view the corrupt block contents with the block editor  BBED utility, working with Oracle technical support to repair the corruption.

If this is a production or test database, your first call should be to get the disk repaired and restored (if applicable) and to open a severity "one" service request on MOSC

Oracle data corruption can occur in a table or index.  Index corruption can be fixed by dropping and rebuilding the index (if possible) .  You can also run some of the Oracle utilities for finding and fixing data corruption issues.

There are three ways to repair corrupt blocks in Oracle: 

a). dbms_repair to repair corruption:  dbms_repair to repair bad blocks

b). BBED to repair corruption Using BBED to fix corrupt blocks 

c). RMAN repair corruption Repair corrupt Oracle block with RMAN

47. How to recover the data, If  the blocks are corrupted due to system problem?

The blockrecover command is no longer used in Oracle 11g and beyond.  In RMAN, the blockrecover command is used with RMAN scripts. 

RMAN tell us the exact data file and relative block number for the corruption.

RMAN> blockrecover datafile 4 block 76;

48. How to speedup the RMAN backup time?

a). Use an incremental backup strategy with block change strategy or

b). Use fileperset, maxopenfiles, diskratio, or 

c). Set  large pool memory size...

49. How would  you speed up the  RMAN backup of a 500 GB database?

We can use       incremental backup either differential  or accumulate

50. How can I  speed up more than 50 TB database backup?

a). Before starting  backup allocate more channels and parallelism, ensure SGA
should  have sufficient amount  of LARAGE POOL and BACKUP_TAPE_IO_SLAVES to true.

b). Do not  perform direct backup to tape. Perform the backup to  flash recovery area (disk) and then perform  the backup of flash  recovery  area  to tape by using rman command BACKUP RECOVERY AREA