Backup optimization specifies that files can be omitted from the backup in some circumstances if an identical copy of the file has already been backed up.
Backup optimization is an RMAN parameter which is specified using the CONFIGURE parameter.
RMAN> CONFIGURE BACKUP OPTIMIZATION ON;
Backup optimization can be used with following operations:
Only one type of channel can be allocated - disk and tape channels cannot be specified in the same backup command.
RMAN determines that a file is identical to one that has already been backed up based on the following rules:
In addition RMAN considers both the retention policy and backup duplexing when determining if a file can be skipped.
Backup optimization can be overridden using the FORCE option. For example:
RMAN> BACKUP DATABASE FORCE; RMAN> BACKUP ARCHIVELOG ALL FORCE;