I have another test server based on a Raspberry Pi 4B. The Pi boots from SD card and uses about 5W. Add 2 drives in a USB drive bay and power for the setup is now up to 25W.
Did you use a regular desktop power supply? PC power supplies can consume 10-15W or more at idle. To build a low power system you need to find a good low power, high efficiency power supply.
For 10 years my home server used a Corsair VS350; it was fantastic, and very efficient at low power draw. Recently the fan failed. The PSU seems discontinued. The _fan_ seems discontinued. I'm going to try replacing the fan but I don't know much about electronics. As a temporary measure, I got a regular "gaming PC" PSU and it has 10% more power draw, it's not efficient at all.
I've been looking for a replacement PSU, and I can only really find very high power ones - minimum about 550W - for reasonable prices. While you can run a low wattage PC on such PSUs, none of them make very much in the way of efficiency promises; only the highest certification, 80 Plus Titanium, makes efficiency promises for 10% load, e.g. it'll be 90% efficient for a 55W load on a 550W supply. Lower certifications only promise to be e.g. 80% efficient for a 110W load on a 550W supply, and make no promises at all about a 55W or 30W load.
So, how does one buy a good low power, high efficiency PSU, without it costing a fortune?
Just in case: opening PSUs is dangerous without precautions. The capacitors may retain enough charge to kill.
Besides the immediate risk to yourself, a PSU can also pose a fire hazard during operation, e.g. if improperly cooled.
My server at home I actually use a 2.5" drive for the torrent scratch disk since I don't really need speed there I just need something that is always spun up with a moderate amount of space that doesn't use much power.
I like the idea of making compute, storage into appliances if possible locally.
It’s best to use ssds in the machines.
If you want spinning drives put them in a dedicated nas for storage.