053-010

10.Consider the following scenario for your database:
-Backup optimization is enabled in RMAN. The recovery window is set to 7 days in RMAN. The most
recent backup to disk for the TOOLS tablespace was taken on November 3, 2007.
The TOOLS tablespace is read-only since November 4, 2007.
On November 23, 2007, you issue the RMAN command to back up the database to disk. Which statement
is true regarding the backup of the TOOLS tablespace?
A. The RMAN backup fails because the TOOLS tablespace is read-only
B. The RMAN skips the backup of the tablespace because backup optimization is enabled
C. The RMAN makes backup because optimization can be enabled only for backups to disk
D. The RMAN makes the backup because no backup of the tablespace exists within the seven day
window
Answer: D
解析:
Suppose that backup optimization is enabled, and a recovery window backup retention policy is in effect. In this case, when performing SBT backups RMAN always backs up datafiles whose most recent backup is older than the recovery window. For example, assume the following scenario:

1. Today is February 21.
2. The recovery window is 7 days.
3. The most recent backup of tablespace tools to tape is January 3.
4. Tablespace tools is read-only.
On February 21, when you issue a command to back up tablespace tools to tape, RMAN backs it up even though it did not change after the January 3 backup (because it is read-only). RMAN makes the backup because no backup of the tablespace exists within the 7-day recovery window.

This behavior enables the media manager to expire old tapes. Otherwise, the media manager would be forced to keep the January 3 backup of tablespace tools indefinitely. By making a more recent backup of tablespace tools on February 21, RMAN enables the media manager to expire the tape containing the January 3 backup.

参考:
http://docs.oracle.com/cd/B28359_01/backup.111/b28270/rcmconfb.htm#BRADV89437