Onnto RS-M4QO User Manual page 14

9. Hold the HDD with the metal cover side facing you and the handle attached
on the upward position.
When inserting the HDD on its reverse side, the SmartGuider System
won't be able to align and the HDD cannot be inserted.
10. Align the handle with the guide rails and slide the HDD into the indicated slot.
Firmly push downward until a "thump" sound is heard. Repeat the same
procedures for the rest of HDDs.
In most cases, you would need to firmly push the trays to a close until a
"thump" sound is heard.
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