A side loading enclosure for a rack mount type storage unit is provided. The enclosure provides for easier access to hard disk drives (HDDs) for maintenance and repair as well as the ability to increase the number of HDDs that can be mounted in a single enclosure. The enclosure may include a bottom plate, a pair of side plates, and a pair of end plates. Located within the enclosure are a first row, extending perpendicularly between the pair of end plates, having one or more stacks of HDDs mounted to a first printed circuit board and a second row, extending perpendicularly between the pair of end plates, having one or more stacks of HDDs mounted to a second printed circuit board. The one or more stacks of HDDS in the first row is separate from and located parallel to the one or more stacks of HDDs in the second row.