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Oracle RMAN Interview Question

1) Difference between catalog and nocatalog?

ANS: CATALOG is used when you use a repository database as catalog.
NOCATALOG is used when you used the controlfile to register your backup information.
Default in NOCATALOG.

2) Difference between using recovery catalog and control file?

ANS:

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?

ANS:


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?

ANS:

By querying v$rman_status or v$session_longops


5) From where list & report commands will get input

LIST:

The primary purpose of the LIST command is to list backup and copies. For example, you can list:
Backups and proxy copies of a database, tablespace, datafile, archived redo log, or control file
Backups that have expired
Backups restricted by time, path name, device type, tag, or recoverability
Archived redo log files and disk copies

REPORT:

You can use the REPORT command to answer important questions, such as:
Which files need a backup?
Which files have had unrecoverable operations performed on them?
Which backups are obsolete and can be deleted?
What was the physical schema of the target database or a database in the Data Guard environment at some previous time?
Which files have not been backed up recently?


6) Command to delete archive logs older than 7days?

ANS:

RMAN> delete archivelog all completed before sysdate-7;


7) What is the use of crosscheck command in RMAN?

ANS:

Crosscheck will be useful to check whether the catalog information is intact with OS level information.


8) What are the differences between crosscheck and validate commands

ANS:

Use the CROSSCHECK command to synchronize the physical reality of backups and copies with their logical records in the RMAN repository.
Use the VALIDATE command to check for corrupt blocks and missing files, or to determine whether a backup set can be restored.

9) Which is one is good, differential (incremental) backup or cumulative (incremental) backup?

ANS:

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

10) What is Level 0, Level 1 backup?

ANS:

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


11)  Can we perform level 1 backup without level 0 backup?

ANS:

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.


12) Will RMAN put the database/tablespace/datafile in backup mode ?

RMAN does not require you to put the database in backup mode.

13) What is snapshot control file?

ANS:

The snapshot CONTROLFILE is a copy of the CONTROLFILE that RMAN utilizes during long running operation (such as backup). 
RMAN needs a read consistent view of the CONTROLFILE for the backup operation, but by its nature the control file is extremely volatile.  
Instead of putting lock on the control file and causing all kinds of db enqueue problems, RMAN makes a copy of controlfile called snapshot controlfile.  
The snapshot is refreshed at the beginning of every backup.


14) what is controlfile auto backup ?

ANS:

then RMAN automatically backs up the control file and server parameter file after every backup and after database structural changes. 
The control file autobackup contains metadata about the previous backup, which is crucial for disaster recovery.


15) What is the difference between backup set and backup piece?

ANS:

Backup set is logical and backup piece is physical.


16) What is obsolete backup & 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.

17)  What is the difference between hot backup & 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.


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


19)  What is the difference between auxiliary channel and maintenance channel ?


AUXILIARY:
Specifies a connection between RMAN and an auxiliary database instance.
An auxiliary instance is used when executing the DUPLICATE or TRANSPORT TABLESPACE command, 
and when performing TSPITR with RECOVER TABLESPACE . When specifying this option, the auxiliary instance must be started but not mounted.
See Also: DUPLICATE to learn how to duplicate a database, and CONNECT to learn how to connect to a duplicate database instance

CHANNEL:

Specifies a connection between RMAN and the target database instance. 
The channel_id is the case-sensitive name of the channel. 
The database uses the channel_id to report I/O errors.
Each connection initiates an database server session on the target or auxiliary instance: this session performs the work of backing up, restoring, or recovering RMAN backups. 
You cannot make a connection to a shared server session.
Whether ALLOCATE CHANNEL allocates operating system resources immediately depends on the operating system. 
On some platforms, operating system resources are allocated at the time the command is issued. 
On other platforms, operating system resources are not allocated until you open a file for reading or writing.
Each channel operates on one backup set or image copy at a time. 
RMAN automatically releases the channel at the end of the job.

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