Interview Q and A for Oracle Backup and Recovery Part - 4

101. You loss 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 data file and recover datafile.
SQL> alter database create datafile ‘/u01/app/oracle/oradata/xyz.dbf’ size 2G;
RMAN> recover datafile file_id;

102. What is obsolete backup & expired backup?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.

103. 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.

104. What are the Architectural components of RMAN?
RMAN Executables
Sercer process
Channels
Target database
Recovery catalog database (optional)
Media management Layer (optional)
Backups, backup sets and backup pieces

105. What are channels?
A channel is an RMAN server process started when there is a need to communicate with an I/O device, such as a disk or a tape. A channel is what reads and writes RMAN backup files. It is through the allocation of channels that you govern I/O characteristics:
Type of I/O device being read or written to, either a disk or an sbt_tape
Number of processes simultaneously accessing an I/O device
Maximize size of files created on I/O devices
Maximize rate at which database files are read
Maximize number of files open at a time

106. Why is the catalog optional?
Because RMAN manages backup and recovery operations, it requires a place to store necessary information about the database. RMAN always stores this information in the target database control file. You can also store RMAN metadata in a recovery catalog schema contained in a separate database. The recovery catalog schema must be stored in a database other than the target database.

107. What is a Backup set?
A logical grouping of backup files — the backup pieces — that are created when you issue an RMAN backup command. A backup set is RMAN’s name for a collection of files associated with a backup. A backup set is composed of one or more backup pieces.

108. What are the benefits of using RMAN?
Incremental backups that only copy data blocks that have changed since the last backup.
Tablespaces are not put in backup mode, thus there is noextra redo log generation during online backups.
Detection of corrupt blocks during backups.
Parallelization of I/O operations.
Automatic logging of all backup and recovery operations.
Built-in reporting and listing commands.

109. What are the various reports available with RMAN
RMAN>list backup;
RMAN> list archive;

110. In catalog database, if some of the blocks are corrupted due to system crash, How will you recover?
using RMAN BLOCK RECOVER command

111. How do you enable the autobackup for the controlfile using RMAN?
Issue command at RMAN prompt.
RMAN> configure controlfile autobackup on;
Also we can configure controlfile backup format.
RMAN> configure controlfile autobackup format for device type disk to ‘$HOME/BACKUP/RMAN/ F.bkp’;

112. How do you identify what are the all the target databases that are being backed-up with RMAN database?
You don’t have any view to identify whether it is backed up or not. The only option is connect to the target database and give list backup this will give you the backup information with date and timing.

113. How do you identify the block corruption in RMAN database? How do you fix it?
Using v$block_corruption view you can find which blocks corrupted.

RMAN> block recover datafile <fileid> block <blockid>;

Using the above statement You recover the corrupted blocks. First check whether the block is corrupted or not by using this command

SQL>select file# block# from v$database_block_corruption;
file# block
2 507
the above block is corrupted…
conn to Rman
To recover the block use this command…
RMAN>blockrecover datafile 2 block 507;
the above command recover the block 507
Now just verify it…..
Rman>blockrecover corruption list;

114. How do you clone the database using RMAN software? Give brief steps? When do you use crosscheck command?
Check whether backup pieces proxy copies or disk copies still exist.
Two commands available in RMAN to clone database:
1) Duplicate
2) Restore.

115. 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

116. How do you install the RMAN recovery catalog?
Steps to be followed:
1) Create connection string at catalog database.
2) At catalog database create one new user or use existing user and give that user a recovery_catalog_owner privilege.
3) Login into RMAN with connection string
a) export ORACLE_SID
b) rman target catalog @connection string
4) rman> create catalog;
5) register database;

117. What is the difference between physical and logical backups?
In Oracle Logical Backup is “which is taken using either Traditional Export/Import or Latest Data Pump”. Where as Physical backup is known “when you take Physical O/s Database related Files as Backup”.

118. How to enable Fast Incremental Backup to backup only those data blocks that have changed?
SQL> ALTER DATABASE enable BLOCK CHANGE TRACKING;

119. How do you set the flash recovery area?
SQL> ALTER SYSTEM SET db_recovery_file_dest_size = 100G;
SQL> ALTER SYSTEM SET db_recovery_file_dest = ‘/u10/oradata/school’;

120. What is auxiliary channel in RMAN? When do you need this?
An auxiliary channel is a link to auxiliary instance. If you do not have automatic channels configured, then before issuing the DUPLICATE command, manually allocate at least one auxiliary channel within the same RUN command.

121. How do you use the V$RECOVERY_FILE_DEST view to display information regarding the flashrecovery area?
SQL> SELECT name, space_limit, space_used,space_reclaimable, number_of_filesFROM v$recovery_file_dest;

122. How can you display warning messages?
SQL> SELECT object_type, message_type,message_level, reason, suggested_actionFROM dba_outstanding_alerts;

123. How do you backup the entire database?
RMAN> BACKUP DATABASE;

124. How do you backup an individual tablespaces?
RMAN> CONFIGURE DEFAULT DEVICE TYPE TO DISK;
RMAN> BACKUP TABLESPACE system;

125. How do you backup datafiles and control files?
RMAN> BACKUP DATAFILE 3;
RMAN> BACKUP CURRENT CONTROLFILE;

126. How to perform fast recovery of database?

Use a fast recovery without restoring all backups from their backup location to the location specified in the controlfile.
RMAN> SWITCH DATABASE TO COPY;

127. Is there a separate background process for writing flashback logs?
Yes. RVWR (Recovery Writer, a.k.a Flashback Writer) was introduced in Oracle 10g to write flashback data from the Flashback Buffer in the SGA to the flashback database logs on disk.