If you've got a copy of the data that's local, why are you opening up ports? Just run the backup job internally.

I'm also not fond of using SBCs as a NAS, by nature their I/O is extremely limited. It will probably work as a backup, but man do I not trust a USB interface at all.

I also recommend not relying on email for notifications - too unreliable. I use the healthchecks.io docker image and have it send me notifications via Pushover when something fails.

A few thoughts on this:

• Debian is, in my opinion, oversized for an OPZ2. If it absolutely has to be Linux (does it?), Alpine or Void might be worth a closer look.
• Why SFTP? Wouldn't SCP be enough?
• Automatic updates are risky for a device that is supposed to run always. Instead, I would recommend sending update notifications and then manually applying an update from time to time. If the device no longer boots up, you often don't even notice it.

Syncthing

Hi,

maybe use openwrt, it’s meant by to be used on cheap low end devices, don’t know how good the image is. https://github.com/Kazagumo/openwrt-orangepizero2

I personally use it on an discontinued WD mybook live duo. If you prefer an easy setup, be warned, it is not. ;) On the plus side, openwrts Luci is a good starting point for configuring of a lot of services, hdd spin down, monitoring, etc.

Use case: samba4, kopia destination from my VPS through Zerotier

Good luck with your setup!