Asus RS160-E4/PA4 - Manual (Page 143)

ASUS RS160-E4/PA4 6-
5.2.8. Selecting.the.boot.drive.from.a.RAID.set
You must have created a new RAID configuration before you can select the
boot drive from a RAID set. Refer to the Creating.a.RAID.set:.Using.New.
Configuration section for details.
To select the boot drive from a RAID set:
1. From the Management.Menu, select Configure > Select.Boot.Drive, then
press <Enter>.
2. When prompted, use the arrow keys to select the bootable logical drive from
the list, then press <Enter>.
3. The logical drive is selected as boot drive. Press any key to continue.