In a mass storage library, a module storage array includes a back plate having "T" shaped apertures patterned to form a cartridge storage together with cell blocks that have "T" shaped protrusions to fit into the openings in the back plate. A column of cell blocks are held in place between a shelf and a spring load. Interlocking surfaces molded into the cell blocks assist in holding the column of cell blocks in place with the "T" shaped protrusions and openings in the back plate. The cell blocks are stacked on the shelf with the "T" shaped protrusions inserted into the openings in the back plate and their mating surfaces interlocked. The spring load clamps the cell against the shelf. The cell blocks form cavities that hold the cartridges in the storage array. A plurality of columns of cell blocks provide the complete storage array. Calibration targets are provided to align the cell blocks to the library accessor and reader. One strip the length of the storage cell stack contains a bar-code viewable through each cartridge storage cell and scannable by an accessor scanner to identify the individual cell blocks.