QUESTION 148
You want to back up your 100-GB database on a remote tape device. You are required to ensure that minimum
network bandwidth is consumed while transferring the backups to the tape device. The current consumption of
your CPU is approximately 40 percent.
Which type of backup should you perform?
A. standard backup set
B. image copy
C. compressed backup
D. user-managed backup
Answer: C
同485题：http://blog.csdn.net/rlhua/article/details/15029069
Explanation/Reference:
Section: Backup, Recovery & Recovery Manager (RMAN)
In this scenario, you should use a compressed backup. The size of the database in this scenario is large, and
you are required to reduce the network bandwidth consumed while the backups are being transferred to a
remote tape device. A compressed backup will reduce the size of the database backup and will eventually
reduce the network bandwidth consumed to place the backup on a remote tape device. The CPU usage in this
scenario is low. Therefore, the CPU can tolerate some overhead that will be generated while compressing
backups. You can only perform compression on backup sets, but not on image copies. Other situations in
which compressed backups can be beneficial are as follows:
- When there is a space constraint on the backup disk.
- When writing backups either to a CD or a DVD
- When you want to limit the expense of backup media
You should not use a standard backup set in this scenario because a standard backup set is larger and will
consume more network bandwidth when it is being placed on a remote tape device. A standard backup set
should be used if CPU performance is more important than the benefits provided by a compressed backup. A
compressed backup incurs some CPU overhead and should not be used if CPU performance cannot be
compromised.
You cannot use an image copy in this scenario. You cannot create an image copy on tape devices. An image
copy can be created only on disk. An image copy is an identical copy of a datafile in the database and is
created using RMAN commands. An image copy is larger than a backup set because the unused data blocks
are also copied in an image copy. Image copies should be used when you want to simplify the recovery
process.
You should not use user-managed backup in this scenario. The user-managed backup will be larger than a
compressed backup. A user-managed backup creates an exact copy of a datafile using operating system
commands, and copies all the used and unused blocksin the datafile. This increases the size of the backups.
In this scenario, you are required to reduce the network bandwidth consumed. Therefore, you should choose a
backup method that reduces the size of the backups.