Exercise : RMAN

                RMAN Interview Questions

1. What is RMAN ?
Recovery Manager (RMAN) is a utility that can manage your entire Oracle backup and recovery activities.

Which Files must be backed up?
Database Files (with RMAN)
Control Files (with RMAN)
Offline Redolog Files (with RMAN)
INIT.ORA (manually)
Password Files (manually)

 2.   When you take a hot backup putting Tablespace in begin backup mode, Oracle records SCN # from header of a database file.  What happens when you issue hot backup database in RMAN at block level backup? How does RMAN mark the record that the block has been backed up ?  How does RMAN know what blocks were backed up so that it doesn't have to scan them again?

In 11g, there is Oracle Block Change Tracking feature.  Once enabled; this new 10g feature records the modified since last backup and stores the log of it in a block change tracking file. During backups RMAN uses the log file to identify the specific blocks that must be backed up. This improves RMAN's performance as it does not have to scan whole datafiles to detect changed blocks.
Logging of changed blocks is performed by the CTRW process which is also responsible for writing data to the block change tracking file. RMAN uses SCNs on the block level and the archived redo logs to resolve any inconsistencies in the datafiles from a hot backup. What RMAN does not require is to put the tablespace in BACKUP mode, thus freezing the SCN in the header. Rather, RMAN keeps this information in either your control files or in the RMAN repository (i.e., Recovery Catalog). 

3.  What are the Architectural components of RMAN?

1.RMAN executable
2.Server processes
3.Channels
4.Target database
5.Recovery catalog database (optional)
6.Media management layer (optional)
7.Backups, backup sets, and backup pieces

4.  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 such as:

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

Maximum size of files created on I/O devices

Maximum rate at which database files are read

Maximum number of files open at a time

5.  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.

6.  What does complete RMAN backup consist of ?
A backup of all or part of your database. This results from issuing an RMAN backup command. A backup consists of one or more backup sets.

7.  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.

8.  What is a Backup piece?
A physical binary file created by RMAN during a backup. Backup pieces are written to your backup medium, whether to disk or tape. They contain blocks from the target database's datafiles, archived redo log files, and control files. When RMAN constructs a backup piece from datafiles, there are a several rules that it follows:

·       A datafile cannot span backup sets

·       A datafile can span backup pieces as long as it stays within one backup set

·       Datafiles and control files can coexist in the same backup sets

·       Archived redo log files are never in the same backup set as datafiles or control files RMAN is the only tool that can operate on backup pieces. If you need to restore a file from an RMAN backup, you must use RMAN to do it. There's no way for you to manually reconstruct database files from the backup pieces. You must use RMAN to restore files from a backup piece. 

9.  What are the benefits of using RMAN?

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