2 Overview of the RMAN Environment

Installed with the database, Recovery Manager (RMAN) is an Oracle database client which performs backup and recovery tasks on your databases and automates administration of your backup strategies. It greatly simplifies backing up, restoring, and recovering database files.

The RMAN environment consists of the utilities and databases that play a role in backing up your data. At a minimum, the environment for RMAN must include the following:

The target database to be backed up;
The RMAN client, which interprets backup and recovery commands, directs server sessions to execute those commands, and records your backup and recovery activity in the target database control file.

Some environments will also use these optional components:

A flash recovery area, a disk location in which the database can store and manage files related to backup and recovery;
Media management software, required for RMAN to interface with backup devices such as tape drives;
A recovery catalog database, a separate database schema used to record RMAN activity against one or more target databases.

About the Target Database

The target database is the database that you are backing up, restoring, or recovering with RMAN.

About the RMAN Client

RMAN is a command-line-oriented database client, much like SQL*Plus, with its own command syntax. From the RMAN client you can issue RMAN commands and SQL statements to perform and report on backup and recovery operations.

RMAN can take interactive input or read input from plain text files (called command files). RMAN then communicates with one or more server processes on the target database server which actually perform the work. You can also access RMAN through the Enterprise Manager; for details see Oracle Enterprise Manager Administrator's Guide.

The RMAN executable is typically installed in the same directory as the other database executables. On Unix systems, for example, the RMAN executable is located in $ORACLE_HOME/bin.

About the RMAN Repository

RMAN maintains metadata about the target database and its backup and recovery operations in the RMAN repository. Among other things, RMAN stores information about its own configuration settings, the target database schema, archived redo logs, and all backup files on disk or tape. RMAN's LIST, REPORT, and SHOW commands display RMAN repository information.

The primary store for RMAN repository data is always the control file of the target database. The CONTROL_FILE_RECORD_KEEP_TIME initialization parameter controls how long backup records are kept in the control file before those records are re-used to hold information about more recent backups.

Another copy of the RMAN repository data can also be saved in the recovery catalog.

About the Recovery Catalog

Using a recovery catalog preserves RMAN repository information if the control file is lost, making it much easier to restore and recover following the loss of the control file. (A backup control file may not contain complete information about recent available backups.) The recovery catalog can also store a much more extensive history of your backups than the control file, due to limits on the number of control file records.

In addition to RMAN repository records, the recovery catalog can also hold RMAN stored scripts, sequences of RMAN commands for common backup tasks. Centralized storage of scripts in the recovery catalog can be more convenient than working with command files.

Except for stored scripts, all of RMAN's features work equally well with or without a recovery catalog. For more information on the recovery catalog see Oracle Database Backup and Recovery Advanced User's Guide.

About the Flash Recovery Area

The Automatic Disk-Based Backup and Recovery feature simplifies managing disk space and files related to backup and recovery, by managing all backup and recovery related files in a flash recovery area. You set the flash recovery area location and size on disk, using the DB_RECOVERY_FILE_DEST and DB_RECOVERY_FILE_DEST_SIZE initialization parameters. You also specify a retention policy that dictates when backups may be discarded. RMAN then manages your backup storage, deleting obsolete backups and backups already copied to tape when space is needed, but keeping as many backups on disk as space permits. This minimizes restores from tape during data recovery operations to shorten restore and recovery times.

About Media Managers

To access sequential media devices like tape libraries, RMAN uses third-party media management software. A media manager controls these devices during backup and recovery, managing the loading, labeling and unloading of media, among other functions. Media management devices are sometimes called SBT (system backup to tape) devices.

The Oracle Backup Solutions Program (BSP) works with vendors to help them produce media management software for their devices. For enterprises that already use media management software in their environment, many of those software products can be directly integrated with RMAN. Contact your media management software vendor for details about whether they participate in the BSP and have an RMAN-compatible media management layer.

About RMAN Channels

RMAN uses server sessions on the target database instance to perform all backup, restore and recovery operations. Each server session used by RMAN is known as an RMAN channel.

A channel can be either a disk channel, used for backup tasks that perform disk I/O, or an sbt channel, which is used to interact with media managers.

At the beginning of a series of RMAN commands, you can use the RMAN ALLOCATE CHANNEL command to allocate channels, specifying the number of server sessions to use for the tasks, and settings that affect the behavior of each server session. (Note that to use ALLOCATE CHANNEL you must group the commands for which the allocated channels apply using a RUN block. The RMAN RUN command is described in "Controlling Scripts: The RUN Command".)

You can also use the RMAN CONFIGURE command to configure channels, specifying persistent settings for the channels RMAN should allocate by default if you do not explicitly allocate channels for a particular task. The channels allocated as a result of configured settings are sometimes referred to as automatic channels. If any channels are explicitly allocated then the configured channel settings are ignored.

The number of channels that are used for an RMAN job controls the amount of work that is run in parallel. When backing up or restoring files, RMAN automatically schedules the work to make the most use of all the available channels.

One disk channel is immediately started when RMAN first connects to the target database, and remains as long as RMAN is connected. This channel, known as the default channel, is not used for tasks involving bulk data transfer, such as backup or restore of database files.