Explanation of RMAN Commands

Explanation of RMAN Commands

  TARGET DATABASE – A Target Database is the primary database that will be backed up for standby database creation. In RMAN’s terminology, the term target database identifies the database that is undergoing a backup, restore or recovery operation by Recovery Manager.

AUXILIARY DATABASE – An Auxiliary Database is a standby database that will be created as a result of the duplication of the target database. In RMAN’s terminology, Auxiliary instance identifies an instance which RMAN connects in order to execute the duplicate command.

CHANNEL – A Channel is a communication pipeline between a RMAN executable and a target or auxiliary database. A channel consists of a server session on the target or auxiliary database and a data stream from the database to the backup device or vice-versa. RMAN console sends commands to the database using this channel, and the server session running on the database executes the command on behalf of Recovery Manager. Some degree of parallelism during the backup or restore operation can be achieved using multiple channels.

AUTOMATIC CHANNEL ALLOCATION  – RMAN Channels can be configured to use a set of default attributes for each operation when a channel is not allocated manually. This set of channels is persistent and can be configured using the CONFIGURE command. When such a set of channels is pre-defined, it is called automatic channel allocation. By default, RMAN configures a channel of device type, DISK, to be used for automatic channel allocation.

MANUAL CHANNEL ALLOCATION   - As the name suggests, a channel can be configured manually for special needs such as increasing the degree of parallelism. Channels can be allocated manually by using the ALLOCATE CHANNEL command in the RUN block of RMAN statement.

DUPLICATE COMMAND – To restore a backup set or image copy, the DUPLICATE command can be used. The duplicate command always performs a complete restoration of the target database. Using this command, a database can be restored on the local host sharing with the target database or on remote host. A recovery catalog is not needed to use the duplicate command.  It can be used with the control file of the target database serving as the repository.

BACKUP SET – Recovery Manager backs up the datafiles, control file, archived log files, and server parameter files in a RMAN specific format called backup pieces. A set of one or more such backup pieces makes up a backup set. A backup set is created using the BACKUP command.

IMAGE COPY – As opposed to the backup set, an image copy is not a RMAN specific format. It is a replica of an actual file. Image copies are created using the COPY command.

SET NEWNAME   – This command can be used to rename the data files to be restored to a new location. It is equivalent to the db_file_name_convert  parameter of the server initialization parameter file. Combination of the SET NEWNAME and SWITCH command is the equivalent of the ALTER DATABASE RENAME FILE statement.

CONFIGURE AUXNAME   – CONFIGURE AUXNAME is equivalent to the SET NEWNAME  command, except that the CONFIGURE AUXNAME is persistent, whereas, the SET NEWNAME command must be used every time the DBA wants to rename a data file. It is necessary to connect to the recovery catalog in order to use the CONFIGURE AUXNAME command.

DORECOVER   – When the DUPLICATE command is specified with the DORECOVER option, it starts recovery after restoration. The recovery is performed using all available archived redo logs and incremental backups. This is the recommended option while creating standby databases using recovery manager. This will save the extra step of recovering the standby database once it is created.

NOFILENAMECHECK  – It is an option for the DUPLICATE command. When NOFILENAMECHECK is used with the DUPLICATE command, RMAN does not validate the filenames during restoration. If the primary database and the standby database are on the same host, this option should not be used.

Thanks
Srini