A storage system is provided for storing data for a computer system where the storage capacity can be incrementally increased without disrupting the operations of the storage system. The storage system comprises a base unit, and a plurality of modular units. The modular units are inserted into the system as increased storage capacity is required. Each modular unit has an enclosure comprising top, bottom, and side walls. The bottom and top walls each have at least one power connector and data transmission connector. The bottom wall of a first modular unit enclosure attaches to the base unit enclosure and the top wall of the first modular unit enclosure can attach to the bottom wall of a second modular unit enclosure. At least one back plane is provided in each modular unit for providing attachment for a set of storage devices. A data transmission interconnect system is provided for transmitting data and commands between the plurality of storage devices in the modular units and an external source, such that in the event of a loss of connection to any one set of storage devices data and commands can still be transmitted from and to any other set of storage devices.