In one embodiment, an inventory storage module has a first conveyor segment, a second conveyor segment spaced below the first conveyor segment, a first vertical lift disposed at a first end of the module, and a second vertical lift disposed at a second end of the module. The first and second lifts each transfer inventory carriers between the first and second conveyor segments. The first conveyor segment, the second conveyor segment, the first vertical lift, and the second vertical lift together define a conveying loop in a vertical plane, and the storage module translates inventory carriers around the conveying loop until a desired one of the inventory carriers is presented at one of the first and second module ends. An inventory item can be retrieved from, or stowed in, the desired one of the inventory carriers at the one of the first and second module ends.