Sorry, because this becomes way too much for a casual conversation.
Yes, because Nextcloud performs much better.
No, I would actually skip usb hard drives altogether because they are much slower than nvme.
In this game that is nothing. Unfortunately, even the $6tb mirrored disks will cost you around 300 - $400.
In that case I would ditch the Pi. Sell it to someone for what you paid for it.
That is not good. And the Pi 5 simply cannot compete with a regular server, especially once you want to add disks of janky usb to be used in production. (I have done exactly this over many, many years).
OpenZFS is designed for disk mirroring and data snapshots. It is designed to do exactly what you are seeking, but it is still contingent on hardware, as a successor to RAID.
Ubuntu now natively supports it, but so do nas platforms like Truenas.
Use the Pi 5
Spent another $30 on the nvme adapter and buy an nvme disk (2tb is $110).
Now you are at $140 - $240, but the Pi 5 will run at maximum speed over a 1gb connection.
Add a 6tb disk for $100 - $150 more for backups, but now you’ve spent close to $400.
This is really all you can ask for.
Don’t use the Pi 5? Ditch it for a proper server
Correct, if your goal is mirrored disks…
- Sell the Pi 5.
- Buy an old tower machine off Craigslist
- Buy an ssd, of an ssd within a usb 3 housing, of 32gb ($10 - $20) to boot Truenas Scale
- Shuck your hard disks, by removing them from the enclosure.
- Install in your tower pc over proper sata
- Add 6tb to Truenas as a mirror pool
It can run Nextcloud, and you simply select the pool you wish to use for your data.
- I recommend buying somemore ram, at least 32gb to comfortably run Nextcloud on top of Truenas.
- Add as many more disks and pools as you want
- Snapshots and backups are all supported through a friendly GUI.
Now your sata disks will perform at maximum speed and you can expand at will.
^^ If this is your goal you should get proper hardware.
Otherwise, I recommend the nvme adapter and one nvme disk.
You can add a usb disk for backups, but at that point… consider whether it is time for the much stronger Truenas!