Apparatus for storing data and supplying stored data comprising a main housing containing control circuitry for controlling signals to a plurality of disk drives. The main housing has a plurality of mounting mechanisms each configured to support a unit of a first type. The apparatus further comprises a plurality of cables each having a first connector for connecting to a unit of the first type for providing signals from the control circuitry. The apparatus has a first unit, of a first type, having a plurality of second connectors each connected to a disk drive and a fan providing a flow of air for cooling the disk drives and the control circuitry. The first unit is connected to a first one of the cables and mounted in a first one of the mounting mechanisms such that the first unit is mounted to slide into the main housing. The apparatus also has a second unit, of a second type, supported by a second one of the mounting mechanisms and mounted to slide into the main housing. The second unit is connected to a second one of the cables and has a fan providing a flow of air for cooling the control circuitry. The second unit is removable from the main housing and replaceable by a unit of the first type.