The RMAN ecosystem consists of many different components. Figure 13-1 shows the interactions of the main RMAN pieces. Refer to this diagram when reading this section.
Figure13-1.RMAN architectural components
The following list describes the RMAN architectural components and definitions:
• DBA: This is the human interaction to ensure successful backups and restores.
• Target database: This is the database that is being backed up by RMAN. You connect to the target database with the RMAN command line’s TARGET parameter (see the next section for more details).
• RMAN client: This is the rman utility from which you issue BACKUP, RESTORE, and RECOVER commands. On most database servers, the rman utility is located in the ORACLE_HOME/bin directory (along with all the other Oracle utilities, such as sqlplus and expdp).
• Oracle server processes: When you execute the rman client and connect to the target database, two Oracle server background processes are started. The first default server process interacts with the PL/SQL packages to coordinate the backup activities. The secondary polling process occasionally updates Oracle data dictionary structures.
• Channels: This is the Oracle server processes for handling I/O between files being backed up (or restored) and the backup device (disk or tape).
• PL/SQL packages: RMAN uses two internal PL/SQL packages (owned by SYS) to perform backup and restore tasks: DBMS_RCVMAN and DBMS_ BACKUP_RESTORE. DBMS_RCVMAN accesses information in the control file and passes that to the RMAN server processes. The DBMS_BACKUP_ RESTORE package performs most of RMAN’s work. For example, this package creates the system calls that direct the channel processes to
perform B&R operations.
• Memory buffers (PGA or SGA): RMAN uses a memory area in the PGA (and sometimes in the SGA) as a buffer when reading from data files and copying subsequent blocks to back up files.
• Auxiliary database: RMAN restores target database data files to this database for the purpose of duplicating a database, creating a Data Guard standby database, or performing a database point-in-time recovery (DBPITR).
• Backup/back up: This word can be either a noun or a verb. The physical files (backup) store the backed-up files; the act of copying and archiving files is backing up. Backups can consist of backup sets and backup pieces or image copies.
• Backup set: When you run an RMAN BACKUP command, by default it creates one or more backup sets. A backup set is a logical RMAN construct that groups backup piece files. You can think of the relationship of a backup set to a backup piece as similar to the relationship between a tablespace and a data file: one is a logical construct, and the other is a physical file.
• Backup piece file: This is an RMAN binary backup file. Each logical backup set consists of one or more backup piece files. These are the physical files that RMAN creates on disk or tape. They are binary, proprietary format files that only RMAN can read or write to. A backup piece can contain blocks from many different data files. Backup piece files are typically smaller than data files, because backup pieces contain only blocks that have been used in the data files.
• Image copy: This is initiated with the BACKUP AS COPY command. It is a type of backup in which RMAN creates identical copies of a data file, archivelog file, or control file. Image copies can be operated
on by OS utilities such as the Linux cp and mv commands. Image copies are used as part of incrementally updated image backups. Sometimes, it is preferable to use image copies rather than backup sets if you need to be able to restore quickly.
• Recovery catalog: This optional database schema contains tables used to store metadata information regarding RMAN backup operations. Oracle strongly recommends using a recovery catalog, because it provides more options for backup and restore. The catalog is normally remote and does not have to be in each of the databases.
• Media manager: This third-party software allows RMAN to back up files directly to tape. Backing up to tape is desirable when you do not have enough room to back up directly to disk or when disaster recovery requirements necessitate a backup to storage that can be easily moved offsite.
• Fast recovery area (FRA): This is a disk area that RMAN can use for backups. You can also use the FRA to multiplex control files and online redo logs. You instantiate a fast recovery with the database
initialization parameters DB_RECOVERY_FILE_DEST_SIZE and DB_ RECOVERY_FILE_DEST.
• Snapshot control file: RMAN requires a read-consistent view of the control file when either backing up the control file or synchronizing with the recovery catalog (if it is being used). In these situations, RMAN first creates a temporary copy (snapshot) of the control file. This allows RMAN to use a version of the control file that is guaranteed not to change while backing up the control file or synchronizing with the recovery catalog being used).
