Asus RS120-E4/PA2 - Manual (Page 118)

6-12 Chapter 6: RAID configuration
4. Select all the drives required for the RAID set, then press <Enter>. The
configurable array appears on screen.
5. Press <F10>, select the configurable array, then press <SpaceBar>.
Press <F10> again, the logical drive information appears including a Logical
Drive menu that allows you to change the logical drive parameters.