Hey chsvfr,
very interesting I think I saw it too once when I checked for all the compact low power boards with J processors, but always sticked with the ones that had 4 Sata connectors. I also saw some low power server boards but they were way to expensive.
Yeah, all these boards you sadly can't upgrade, but I guess even when you get a normal mainboard and cpu you probably won't upgrade into the same gen usually, since you should already know beforehand how much performance you will need and stick with that until a new mainboard and cpu gen.
I don't know if you saw it, but I already went with the J5040 in a Node 304 case a few days ago and spent the whole weekend setting up my first Unraid server. So far the J5040 seems perfect for what I want to do with the machine, it can run several dockers without no problem it seems, file transfers always hit gigabit speed, even without cache drive used and it is even good enough for running a Windows VM and Plex, while hopefully not using too much energy during idle.
You are right about trying to use the least amount of drives as possible that is why I plan to get like 2x 4TB or 8TB drives as data drives.
Right now I am running it with 2x2TB data drives 1x4TB parity drive 1x500GB SSD for cache and everything works fine, like dockers and vms are on the cache so the drives spindown when not being used and only the ssd has to run, protecting the hdds from mechanical wear over time.
Therefore thank you very much again for your feedback and helping me out deciding for a build.
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For others, who might be researching for low power builds too.
My current Unraid build:
Power Supply: Be quiet! Pure Power 11 FM 550 Watt 80+ Gold Modular BN317
Parity Drive: Seagate IronWolf 4TB HDD ST4000VNZ06
Data HDDs: 2TB WD Green (WD20EZRX) & 2TB WD Red (WD20EFRX)
SSD Cache: 500GB Samsung 850 EVO
RAM: Corsair Vengeance SODIMM 16GB (1x16GB) DDR4 2666MHz CL18
Case: Fractal Design Node 304 black
CPU & Mainboard: ASRock J5040-ITX Mini-ITX Mainboard Intel Quad-Core J5040
Power consumption:
Idle all drives, except cache spun down: ~12W
Idle all drives, spun up: ~20W
High usage (70%+ CPU usage): around ~30W
Temperature:
CPU Idle: ~35°C
100% CPU load: ~75°C
HDDs: ~35°C