为了保证船舶航行安全，首先要确定船舶的航向与位置。船舶定位方法按照参照目标可分为（　）。

Immediately after adding a new disk to or removing an existing disk from an ASM instance, you find that the performance of the database goes down initially until the time the addition or removal process is completed, and then gradually becomes normal.
Which two activities would you perform to maintain a consistent performance of the database while adding or removing disks?（）