A system for storing data includes a rack and one or more data storage modules mounted on the rack. The data storage modules may include a chassis, two or more vertically-oriented backplanes coupled to the chassis, two or more mass storage devices coupled to the backplanes, and one or more air passages extending beneath one or more of the backplanes. Each backplane is configured to preclude airflow through the backplane between opposite vertical faces and can couple mass storage devices on one or more of the opposite vertical faces. One or more of the air passages can supply an upwards-directed airflow along one of the opposite vertical faces of a backplane to remove heat from a heat producing component of a mass storage device coupled to the vertical face of the vertically-oriented backplane.