Asus RS120-E4/PA2 - Manual (Page 131)

ASUS RS120-E4/PA2 6-25
6.2.7 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.