I have spent more than 24 hours researching this... many rabbit holes!

As Hugh noted, on the Intel side, ECC awareness is mostly a Xeon thing. AMD is much more supportive, but only with some chipsets/motherboards. ECC memory also comes in 2 flavours:

1) Registered (buffered) 80-bit wide, like https://www.kingston.com/datasheets/KF556R36RB-32.pdf

2) Unregistered (unbuffered) 72-bit wide, like: https://www.kingston.com/datasheets/KSM56E46BD8KM-32HA.pdf

and, as far as I can tell, they are not inter-compatible if you want ECC.

I wanted to take advantage of the NVME SSDs, as they are an order of magnitude faster than SATA, but as I mentioned in another thread, I want RAIDZ3, so I want at least 8 SSDs. So I came across https://www.amazon.ca/Highpoint-SSD7540-PCIe-8-Port-Controller/dp/B08LP2HTX3/ which is supports 8 M.2 SSDs in a single PCIe-x16 socket.... the only drawback is $1660. So I also found https://www.amazon.ca/gp/product/B0863KK2BP/ (and many cheaper ones without fan/heatsink) which supports 4 M.2 SSDs (but requires turning on bifurcation mode) but is just over $100. Great, I thought, I throw 2 of those in, and I'm good to go.... so I went off and looked for ECC-supporting motherboards with 2 PCIe-x18 slots. But when I looked at that adapter closely, I discovered I needed to worry about PCI Express lanes!

https://linustechtips.com/topic/1497718-basics-about-pci-lanes-chipset-lanes-and-cpu-lanes-help-for-newbie/ has a good explanation about these, but the bottom line is that these are how the PCIe devices get access to memory via the CPU. Intel Core chips have 20, Ryzen have 24 usable (Xeon and ThreadRipper have 100+). So I went off and looked at Xeon and ThreadRipper chips and motherboards for a while.... but my budget didn't extend that far, and this *is* supposed to be mainly a file server. So I could only have 1 of those 4x M.2 interface boards. So I ended up looking at boards with 1 PCIe-x16, and 4 M.2-x4 slots. Because of the 4-lanes fewer connections of Intel, this basically brought me to Ryzen.

So I ended up with:

1x ASUS Prime X670E-PRO WiFi motherboard (considered Asrock X670E Taichi but couldn't source it)

1x AMD Ryzen™ 7 7700 8-Core CPU - 35 watts, includes cooler

2x Kingston Server Premier 32GB 5600MT/s DDR5 ECC memory

1x ASUS Hyper M.2 x16 Gen 4 PCIe adapter

1x TEAMGROUP T-Force Z540 2TB SSD

7x TEAMGROUP MP44 2TB SSDs

1x SAMA 850W ATX3.0 Fully Modular 80 Plus Gold power supply - even though 350W woul do

1x Corsair 4000D Airflow CC-9011201-WW White mid-tower case

Total with taxes, just over $3000.

Note that this will run mostly headless, apart from maintenance, so I'm more than happy with the built-in Radeon GPU.

I have one high performance SSD which will have small boot and swap partitions. The rest are the best cheap SSDs I could find. All 8 will be mostly a large partition for ZFS for a total of about 10TB of RAIDZ3. I could have doubled that for an additional $1250.

I found https://ca.pcpartpicker.com/list/ very useful, except it doesn't list ECC memory, and doesn't understand PCIe adapters, so it thought I couldn't hook up all my M.2s, and it didn't list the SAMA PSU.

As this has turned out to be a pretty beefy box, I will likely be running Proxmos on top of Debian with ZFS.

../Dave