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I wouldn't go ARM unless you really like tinkering with stuff.

I bought a used Celeron J4105-based system years ago for <100€ and it's doing just fine. The N100 is its successor that should be better in every way.

Don't be afraid to buy cheap used hardware. Especially things like RAM or cases that don't really ever break in normal usage.

Two 4TB HDDs for 120€ each is a rip-off. That's twice what you pay per GB in high capacity drives. Even in the lower capacity segment you can do much better such as 6TB for 100€.

If you have proper (tested!) backups and don't have any specific uptime requirements, you don't need RAID. I'd recommend getting one 16TB-20TB drive then. That would only cost you as much as those two overpriced 4TB drives.

I believe you should buy second hand hardware for that. Can't beat the price and you've tons of gamers and offices trying to get rid of perfectly good hardware for what you're trying to do. I mean a 8th gen i5 CPU will most likely be idle or in low usage most of the time.

I would say to buy i5-8500T or more recent (because you can run a full machine on 8W on that). You can either go for a micro ATX motherboard with that and RAM second hand OR pick an HP Mini ProDesk with the same CPU, both options will be about 130€. Check this example.

The thing with the Minis from HP is that they come with everything, NVME, power supply, ram and ready to go. Most of those more recent machines come with 2x NVME + 1 SATA + USB-C.

If you're comfortable with taking the board out of the case you can place it anywhere and add a M2 to SATA adapter on both NVME slots for about 22€ each and have like 12 SATA HDDs connected to it. If you don't want mess with the hardware you can get a USB DAS for your disks, since it's all USB-C you will not notice any performance impact.

Those machines will outperform your CPU pick by a lot while being cheaper and power efficient on idle.

I recommend going with an N100 based system if you want low power usage. I doubt old workstations that support multiple drives idle near 10W, the mini PC variants might, but they would require a DAS for the HDD's.

I have personally chosen an ASUS N100I-D D4 motherboard with a m.2 to 6x SATA card and it has been working fairly well.

I own an HP Proliant micro server gen 8. Sweet machine. I bought it new, but there are plenty used around, great looking device. A real pro server in a small format. Celeron, but you can find i3, i5, or i7, and can take some specific xeons. 4 real HP drive caddies.an extra sata originally for a CD, that can repurposed for an SSD, and USB3 in case you want to add even more drives. Very low power consumption. I have xpenology installed, because of the polished experience, but you can install any NAS OS you want. Xpenology has a ton of apps you can install, and also does docker.

Earlier this year I built something similar, although with more space for hard drives:

I used the following components:

For storage I bought used 4 TB drives from ebay for around 40 € each.

Now the system is running 5 x 4 TB in RAID 6 as well as a 256 SATA SSD I had laying around as cache.

The system is using 25 Watts in idle with those 5 HDDs, 1 SATA SSD and 2 M.2 SSDs.

It's a bit more you've been asking for but this option would offer you more expandability down there road.

A cheap laptop might also be worth considering? Built in UPS that way, and sometimes UPSes have a large standby power usage. Would support a couple of bus powered drives as well.

Main drawback is no recovery if the battery drains fully.

CWWK N100 - $152

1x16GB Teamgroup elite DDR5-5600 = $37

3x2TB Samsung 990 EVO - $255 1x128GB Patriot P300 -$14 (4TB storage + 2TB parity drive and 128GB for OS)

$7 for some heatsinks for the SSDs.

Total = $465 USD

No idea what those prices look like in Europe.

You also have the option of expanding with 2 SATA ports.

Honestly, they are all good options. I have the Aoostar prebuilt option for my home server/NAS and I have had zero issues with it. 2 Sata SSD's and it's sipping around 12-15W power onload. about 10-11W on idle.

I had the Odroid H3 before that, with same SSD's, it was using about 11-15W under load and about 8W idle.

You have listed some good options there👍 One additional possibility: what about repurposing an old enterprise workstation, like Dell Optiplex, HP Elitedesk, Lenovo Thinkcentre etc.? They can be bought for around 50-100 e/$. For a similar use case I've been running an Optiplex 7010 SFF (Small form factor) with i5 3XXX and 16G of ddr3 and it has been plenty of powerfull for the purpose.

Honestly a raspberry pi or equivalent on diet pi (https://dietpi.com/) is probably a good start. Though with the caveat that you should use its internal utilities to create an off-site backup of your most important data via a provider such as hetzner.

Cheap, low power, and diet pi is Debian with some tweaks so it's very easy to set up either bare metal or via containers (as others have said containers may help manage things easier and safer in the long run).

For storage, you'll probably either need an externally powered USB dock (30ish EUR) or a powered 3.5inch HDD dock if you go this route as the pi cannot reliably power even one SSD from its USB ports - you'll risk IO failures. The same will come from any setup that includes any low power SBC just for stability. In my experience it's still less than 15W but you need stable power for IO stuff on SSDs.

I'm sorry if this is not relevant but I don't have the time to read that whole of text:

https://youtu.be/l30sADfDiM8

I think this is at least similar to what you want to achieve.

Just get a cheap old office PC from eBay or local market place for £50. Add your disks using ZFS (don't use raid as it basically doesn't work in modern systems). I'd be tempted to get one 4tb internal drive and one external usb to use as your backup drive.

For HW I personally use a NUC. If I were to build something today within said budget, I'd go for a second hand thin client.

For example the Thinkcentre M720q Tiny I can buy for 225EUR, coming with 8th gen core i5, 8GiB RAM, 256GiB SSD (1). Idle consumption is around 5W.

HDD's use quite a lot of power and take up a lot of space. I would recommend using SSD's if you have the budget for it.

I've been running my Aoostar R1 for over a year now, no issue at all. ~14W at idle with the 2HDD in standby. 32G RAM, a low power SK hynix Gold P31 1TB NVME. I've re-used the pair of 14TB HDDs from my WD NAS and recently got a pair of 12TB refurbished HDD for ca 240€ to use the old WD NAS as a backup. I run Proxmox with a bunch of LXC containers (12 mostly) of which a pair of pi-hole, pair of VPN/hardened SSH, fileserver, home automation, Logitech media server, Jellyfin etc etc etc The R1 is not that noisy, never crashed once, does not heat up and is powered through a 88.8Wh mini UPS.

Proxmox would still be useful for container management.

Does your budget include the drives you mentioned, or do you already own those? Do you have an esata dock or something already?

You might want to consider used hardware. Should be ca. 50 Bucks+ drives.

Used drives are quite cheap, too. Just use some redundant setup.

No need for virtualization (so no Proxmox, TrueNAS, or Unraid) Run lightweight containers for web services like Immich, Paperless-ngx, Pi-hole, and custom services I’ve developed

Do you not consider containers virtulizations? Or do you plan to run your webservices in the same context? Because I would really suggest against doing the latter.

However, I’m unsure if I really need RAID since I’ll perform regular backups.

Raid is not a backup anyhow ;).

If you don't need the capacity or redundancy of raid I would suggest you buy a single >=8Tb drive. It should be a bit cheaper (For example, I recently payed ~270€ for 16 Tb, which I'd reccomend over paying 240€ for 8Tb in total. There are probably also 8/12 Tb drives for less then 240€.). It will also use half the power as that does not really scale with capacity.

Edit: there are a bunch of 8tb drives at 180€ here for example.