An automated storage and retrieval system includes a storage array of storage locations for case units. An in-out case conveyor is capable of bi-directionally transporting case units to and from the storage array, and an in-out loaded pallet conveyor is capable of bi-directionally transporting loaded pallets towards and away from the storage array. A palletizer-depalletizer cell includes a bi-directional pallet transport system with more than one independently driven pallet transports, each with a different pallet holder independently movable relative to a cell frame. Placement of case units commissioning a pallet layer loading a pallet, and removal of case units decommissioning a pallet layer unloading another pallet are both effected at the common pallet layer interface at a predetermined level of the cell frame. The pallet transports independently index a first and a second of the different pallet holders, each independently holding the pallet loading at the common pallet layer interface.