Making Backups with RMAN - RMAN Recipes for Oracle Database 12c - page 211

When you specify the minimize load clause, RMAN periodically estimates the completion time for a currently
running backup. If RMAN estimates that a backup will complete within the backup window, it slows down the backup
to fit the entire backup window so as to reduce the overhead on the database.
If you're using a tape device to make the backup, you must understand the implications of using the minimize
load clause during backups. When you use the minimize load clause, tape streaming may be below the optimal level
because of the slowing down of the rate of backups by RMAN. Since RMAN has the exclusive use of the tape device
for the entire duration of the backup, you can't use that tape device for any other purpose during the backup. For the
reasons listed here, Oracle recommends that you not use the minimize load option when using a tape drive to make
your backups.
Reusing RMAN Backup Files
Problem
You want to reuse some existing RMAN backup files by overwriting existing backups with new backups.
Solution
You can use the reuse option with your backup commands to enable RMAN to overwrite existing backups, as shown
in the following example:
RMAN> backup reuse database FORMAT '/u01/app/oracle/backup/backup01.rman';
How It Works
When you include the reuse option with a backup command, RMAN will overwrite the existing backups with the newer
backups. The existing backup files, both backup sets and image copies, will be overwritten by a file with an identical
name. You must provide the FORMAT clause, as we showed in the example in the Solution section. Otherwise, the backup
command we showed will create a new backup piece, instead of reusing the existing backup.
Retaining Backups for a Long Time
Problem
You want to retain certain backups beyond what the retention policy for the database will allow for archival purposes.
Solution
Use the keep option with the backup command to retain backups beyond what's mandated by the retention polices
that you've configured. In the following example, the keep until time clause tells RMAN to retain the backup for a
period of six months:
run
{
backup database
tag quarterly
keep until time 'sysdate+180'
restore point '2012Q1';
}