I have a 24/7 file server that's been running for over a decade now. 12 3.5" HDDs in hot-swap cages for 9 or so TiB of usable space (mirrored). I love that thing, it's the most important box in the house, but honestly, it's large, hot, uses a ton of power and I don't know how much longer it can possibly live.

So help me find a worthy successor.

I'd like to stick to Debian (Linux), ZFS, and building it myself using off-the shelf components, but I've only built a couple of desktops for a long time. I don't even know whether one goes for SSDs for data hoarding now (I don't need the sequential speed nor the I/O, but if they're more reliable long-term, sure; or 2.5 " HDDs), let alone whether there's any go-to cases, CPUs, boards, controllers, backplanes ...

I only need like 16 TiB usable space (again, at least mirrored) should serve me well for another few years. CPU should have decent hardware acceleration for the encryption, also the current one is running a couple of VMs, but even a toaster can do that nowadays, I think. I'd like to keep the hot swap; minimise downtime. I work from home and all my important data is on that thing.

Better than Gigabit would be nice, though I don't have any better switches yet. Still copper, though, the existing cables can do 10 Gb/s.

Also, what does one do for backups? Currently I just dump incremental backups over the the network on a separate box in another location, but back when I set this up, cloud services weren't a thing. Is is better to just dump encrypted backups somewhere over the net these days? If so, recommendations?

Feel free to just point me to a decent FAQ/site, obviously. If you want more details, I can do that, too.