Best option I have found so far might be this ASRock 4x4-v2000 https://www.asrockind.com/en-gb/4X4-V2000M , it has an 8-core cpu and supports ECC. Would need to get a M.2 to 4x SATA adapter. The hard part seems to be figuring out how to buy the board itself...
I built my home NAS on this and it's great. Has Oculink ports built into the board so I can just use M.2 for the OS itself and it supports 10 GB ethernet, so as long as I'm wired in, there is effectively no network latency since that's faster than SATA anyway. The board itself also does video, so I can use a Ryzen CPU without Radeon graphics and not have to get the pro to support ECC.
Their new board, the helios64, is bigger, and ECC support was in-progress last time I checked.
Yes, I know that would likely use more electricity, but in my particular case (France), electricity isn't that big of a cost, plus I wouldn't be running this 24/7. More like one or two evenings a week. The only reason why I'm not running recycled "enterprise" servers at home is that my apartment is small and I absolutely cannot stand the noise they make.
This to me is the main issue. Usually, manufacturers think ECC = Enterprise = Running in a computer room = Doesn't need to be quiet.
Of course, usually clients looking for thin, least-possible-U systems doesn't help either.
I've actually gotten my hands on a Lenovo tower server my client wasn't needing anymore which is really pretty quiet. But it's "huge" by rack standards. It's basically a full PC tower in height, but longer.
I could see myself running it in the kitchen or something once I get it home after the lockdowns.
The issue is it only takes 2.5" drives, which are still quite expensive if SSDs or use SMR if HDDs.
* 32bit OS means maximum 16TB Partition Size
* it's not fast at all. It can barely saturate a Gbit connection without any encryption using HTTP. Even with the Crypto Engine enabled, any encryption and the connection drops significantly
* Depending on which version you got, the fans are quite annoying, no matter which version you got, the fans are quite ineffective
* it has at least one known hardware bug concerning SATA and the internal Flash.
* WOL and the internal Watchdog are hit or miss at best
On the other hand the linux support and documentation is top notch so i dont want to complain too much but i am kinda disappointed with the speed i got from it
For the fans - I am not using the included case. I have one stock fan on top of the SOC and one 120mm fan for the disks. The stock fan is decently loud on bootup, but it stops or low-speed during regular operation.
Is that a thing which exists?
Haven't tried it personally, but maybe it works? :)
[1] https://pipci.jeffgeerling.com/cards_storage/iocrest-jmb585-...
In this case, this M.2 slot carries PCIe, so you can add a PCIe SATA controller. Confirm driver support first, of course.