Let’s dive a bit more into how many drives can be operated in typical rackmount form factors. The following numbers are based on front-mounting enclosure devices. There are some rackmount devices that accept drives on the front as well as the rear. Likewise, there are options like having two systems inside one rackmount blade enclosure, including or excluding an optical drive, providing a more featured access panel with I/O interfaces, and so on. Depending on the particular product, there might be fewer drive bays available than listed here.
|Rackmount Server||3.5" Drive Bays||2.5" Drive Bays|
2U servers can accomodate 20 2.5” drives when installed horizontally, or 24 drives if installed vertically. Be aware that the backplanes and drive bays for 2.5" drive solutions require less space than comparable 3.5” products because the drives are much smaller in all three dimensions.
3U solutions usually accept 16 3.5” drives. We haven’t seen many 3U+ solutions designed to run even more 2.5” drves, as even a 2U unit can accept 24 drives.