A hard disk enclosure blade includes an enclosure insertable into a rack, a number of slots, a lever, and a flap. Each slot can receive a tray holding hard disk drives. The lever allows the enclosure to be pushed into and pulled from the rack. The lever has an open position in which the enclosure is removable from the rack, and a closed position in which the enclosure is not removable. The flap has a first flap position in which the flap is disposed across the slots and in which the lever is movable from its closed to its open position, and a second flap position in which the lever is not movable from the closed to the open position. Where the slots are all empty, the flap reverts to the first flap position. Insertion of a tray into a slot forces the flap to the second flap position.