Asus RS120-E4/PA2 - Manual (Page 124)

6-18 Chapter 6: RAID configuration
5. When prompted, use the arrow keys to select Yes from the Initialize? dialog
box, then press <Enter>. You may also press <F10> to initialize the drive
without confirmation.
6. A progress bar appears on screen. If desired, press <Esc> to abort
initialization.
7. When initialization is completed, press <Esc>.