Embodiments generally relate to a optimizing the design of a chassis, such that the chassis features a different width front end hard disk drive module. Key components of the design include chassis flexibility for different hard drive quantities, and sliding rails which can be installed for sliding the chassis in and out of the rack, taking into account the housing contours of both the chassis and the front end hard disk drive module of different width. The rails can be reinforced with different backing materials for improved load support. The sliding rails include an inner set of rails attached to the chassis, and an outer set of rails which extend along the housing of both the chassis and the hard disk drove module.