The weight of the door is carried by rollers running along the upper track. The rollers can be surface mounted or recessed into the door. Both have their advantages, surface mounted are quick and easy to fit and the recessed versions are less visually intrusive because they are routed into the door. In the case of the FD-30H the roller is side-mounted.
Sugatsune sliding doors are super quiet in operation and can have the added refinement of soft-closing at either, neither or both ends of movement.