Comment by j45

24U is about half a rack? 3 feet tall or so. Now, there can be a full length rack (or cage) that has 4 posts, or there's short racks too with just the front 2 posts that can shrink the footprint a lot. This is totally reasonable to find used most places.

Noise and Power Consumption is a huge consideration. I think about it as cost of gpu or computing power per watt. While the information might not be out there, USFF devices like a one or a few Lenovo Thinkcentre m920q works pretty flawlessly with Proxmox or anything else. For a rack, they can be treated as quasi blade servers on a shelf stacked in a rack, or some cases as well. Again, up to most people

These types of USFF devices often have a desktop grade cpu in a mobile setup that is engineering/industrial grade built, and 130w power supplies, and mostly idling. There are newer generations of these types of devices from most of the manufacturers too.

Cost of electricity does add up, but more than that, keeping your wattage footprint low lets you use a more reasonable UPS for battery backup power, if there is a need, it can all stay up much, much longer.