It has 8 hot-swappable SAS bays (also SATA compatible) and I run a Ryzen 9 3900X in 65W eco mode on an AsRock Rack X470 board which has another 8-12 SATA ports (can't remember the exact number, not used because I use an HBA for the bays), so connectivity for storage is high. There's 2 spaces for SATA SSDs on top of the drive bays and you could fit more in various spots if you tried, and 2 NVMe slots on the motherboard.
Also got a single-slot nvidia GPU in there and a 4-port Gb NIC to supplement the 3 existing Gb ports on the board itself (one is dual-purpose for IPMI), some models of the AsRock rack have dual 10G ports too.
It runs most of the time at around 90W which I think is exceptionally low for the performance available, and can go to about double that when the GPU is in use, still very reasonable.
Regarding mainboards - models from CWWK with lots of SATA ports have been trendy lately. But there are reports of problems. The other options are either using some obscure supermicro mainboards with lots of ports or using a HBA for expansion.
I want to mention a possible middle ground here: UGreen NAS Storage. All but the smallest model come the OS on a seperate M.2 drive. If you disable the watchdog in BIOS, you can use the models like a normal Server This would give you:
* 3x M.2 slots * 4, 6 or 8 SATA bays * N100 (4 bay), Pentium Gold 8505 (4 bay), i5-1235u (6 & 8 bay)
The M.2 slots are connected rather slow, but good enough for OS/app drives.
For example, my plan for the next NAS would be the 4-Slot N100 variant with TrueNAS. One M.2 SSD for boot, Two M.2 SSDs for Apps/Server duties in mirroring and the 4 drives in Raid-Z1.
However, once my DS415+ dies, I’m currently more inclined to go with a TerraMaster F4-423 NAS and replace their OS with something else. I’ve read that this TerraMaster model is basically an Intel NUC with a SATA card. And their OS is on a flash drive plugged into an internal USB port - so, very easy to change/replace.
I’ve also read that UGREEN devices should be easy to replace the OS on. So, that’s another option I keep in mind.
Requires a bit of tinkering but the idea of plugging a 1L-format computer to turn it into a multi-disk NAS is quite attractive.
Go to your favorite computer parts retailer website. Go to the Computer Cases category. Filter by desired number of 3.5" bays. Pick from the lot.
[1]: https://www.printables.com/model/866109-200mm-fan-front-for-...
Should save a lot on power and have plenty of muscle for anything you throw at them if you're willing to gamble on the hardware quality.
I have my NAS on a shelf in a mini-ITX case, but it only fits two 3.5" HDDs internally (as well as an SSD, but full-size HDDs are what matter for bulk data storage, the more the better)
Also, it takes a normal full-size ATX PSU because I was fed up a previous case that only had room for its own custom PSU, which kept failing under load. But I note there are now standardised small sizes like TFX12V and LFX12V, are there any efficient and reliable PSUs in these form factors?