348.What does the minimize load database parameter mean when backing up a database?
A. RMAN will attempt to make the backup run as fast as possible without any IO limitations.
B. RMAN will automatically restrict the number of channels in use to one.
C. RMAN will spread the backup IO over the total duration stated in the backup command.
D. RMAN will skip any datafile that currently is involved in an IO operation. RMAN will retry backing up the
datafile later and an error will be raised at the end of the backup if the datafile cannot be backed up.
E. Datafiles will be backed up; those having the lowest current number of IO operations will be backed up
first.
Answer: C

使用了minimize load, RMAN会监测备份时的资源消耗，并定时估计以当前的速度备份要花费多长时间。如果备份估计的完成时间在备份窗口结束之前，RMAN就会降低备份速度以充分利用整个可用的备份窗口。
这降低了与备份有关的数据库的负载。

BACKUP 
  DURATION 4:00 PARTIAL 
  MINIMIZE LOAD 
  DATABASE 
  FILESPERSET 1;

In Example 9-5, RMAN monitors the progress of the running backup, and periodically estimates how long the backup will take to complete at its present rate. If RMAN estimates that the backup will finish before the end of the backup window, then it slows down the rate of backup so that the full available duration will be used. This reduces the overhead on the database associated with the backup.

官方文档：https://docs.oracle.com/cd/B28359_01/backup.111/b28270/rcmbckad.htm