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?（）

You notice a performance change in your production Oracle 12c database. You want to know which change caused this performance difference.
Which method or feature should you use?（）