Databases Reference
In-Depth Information
Chapter 4
Using RMAN
You can start using RMAN to back up and recover your databases with very little fanfare. When you install the Oracle
server software, you'll automatically install RMAN as well. You only absolutely need two things to start using RMAN:
the database you want to back up (referred to as the
target database
) and the RMAN client, which is the interface you
use to interact with the RMAN server processes that perform the actual backup and recovery tasks.
When you use RMAN to back up and recover your database files and objects, you use the RMAN client to interact
with the database. The RMAN client interprets the RMAN commands you issue and starts up the necessary server
sessions to process those commands. The term
RMAN repository
refers to the record of RMAN metadata about all
backup and recovery actions on the target database. RMAN relies on this metadata when it performs backup and
recovery operations.
By default, RMAN always stores a copy of the RMAN repository in the target database's control file. Optionally,
you can also use a
recovery catalog
for long-term storage of the RMAN repository. Whenever there is a change in the
database structure, archived redo logs, or backups, RMAN updates the recovery catalog with the new information
from the target database control file. This way, you have an alternate source for the all-important RMAN repository
data if you lose or can't access the control file of the target database. In addition, the recovery catalog provides a
long-term storage capacity for all RMAN backup and recovery information, whereas such older data is liable to be
overwritten in the control file. The recovery catalog exists as a separate database schema, located ideally in a database
separate from the target database(s). You can simplify your RMAN administration by using a single recovery catalog
for all your Oracle databases.
You start up the RMAN client using the RMAN executable
rman
, which you'll find in the $ORACLE_HOME/bin
directory. In addition to the
rman
executable, RMAN also comes with two other internal components: one a set of
PL/SQL procedures in the target database and the other a file named recover.bsq. RMAN turns the backup and
recovery commands you issue into PL/SQL procedure calls using the recover.bsq file to construct the calls. After you
start the RMAN client, you must log in using either operating system credentials or database authentication. After
logging in, you can issue backup and recovery instructions either by entering RMAN commands at the command line
or by executing a script file that contains RMAN commands. You can also issue several types of SQL commands from
the RMAN command line. After you finish your backup and recovery session, you exit the RMAN client.
In addition to the target database and the RMAN client, the RMAN environment can have other optional elements. If
you follow the Oracle's backup and recovery recommendations (see Chapter 1), you may also have a fast recovery area. In
addition, you must have a media management layer (MML) to interact with tape drives, since RMAN can't work directly
with the tape drives. RMAN can use either a third-party MML or Oracle's own backup and recovery offering, called Oracle
Secure Backup. The MML accesses and controls the tape libraries and manages the loading and unloading of tapes.
Finally, if you plan on working with several databases, it may be a smart idea to use an RMAN catalog database,
which is a separate Oracle database dedicated to storing the recovery catalog. Although the recovery catalog isn't
mandatory, it provides two important advantages over using the database control file to store the RMAN metadata
relating to backup and recovery activity: you can store vastly greater amounts of data in the recovery catalog as
compared to a control file, and you can store RMAN scripts inside the recovery catalog. By default, all RMAN-related
records in the target database's control file are overwritten after seven days, but you can control the length of retention
by setting a higher value for the initialization parameter
control_file_record_keep_time
.
