ZyXEL Communications Network Storage NSA-220 Plus Quick Start Manual page 8

6. Slide the tray back into the disk bay. Make sure the screw hole is at
the top. Push the tray in all the way so the screw hole at the top is
flush with the internal frame.
7. Put the disk tray retaining screw back in.
8. Repeat steps
9. Put the rear panel back on and tighten the thumbscrews.
8
3 to 7 for a second hard drive if you have one.