Backup and Recovery 101 - RMAN Recipes for Oracle Database 12c - page 14

The following list describes the RMAN architectural components:
DBA : Appears somewhat short and bald in the diagram, which isn't far from the truth (in
our case, with the exception of Arup Nanda).
Target database : The database being backed up by RMAN. You connect to the target
database with the RMAN command-line TARGET parameter (more on this in the next
section of this chapter).
RMAN client : The rman utility from which you issue BACKUP , RESTORE , and RECOVER
c ommands. 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, expdp, and so on).
Oracle server processes (channels) : When you execute the rman client and connect to the
target database, two Oracle server background processes are started. One process interacts
with the PL/SQL packages to coordinate the backup activities. The secondary process
occasionally updates Oracle data-dictionary structures. You can query the RMAN metadata
information via views such as V$SESSION_LONGOPS.
PL/SQL packages : RMAN uses two internal PL/SQL packages (owned by SYS) to perform
B&R 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 program global area (and
sometimes in the system global area) as a buffer when reading from data files and copying
subsequent blocks to back up files.
Auxiliary database : A database to which RMAN restores target database data files for the
purpose of duplicating a database, creating a Data Guard standby database, or performing
a database point-in-time recovery.
Channel(s) : Oracle server processes for handling I/O between files being backed up and the
backup device (disk or tape).
Backups and backup sets : When you run an RMAN BACKUP command, it creates one or
more backup sets. A backup set is an internal RMAN construct that logically 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 : RMAN binary backup files. 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're 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 : A type of backup in which RMAN creates identical copies of a data file, archive
redo log 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's preferable to use image copies over backup sets if you need to be
able to restore quickly.