Would it be possible with that app. So i would use one device only for the synching backup sometimes?
Syncthing installed on two devices allows you select what to backup on filesystem (everything is an option) from one device to another device. It does it automatically after initial setup and has a nice easy to use web ui. Second device can be a super cheap Raspberry Pi with a disk running in a different location.
Buying the same drives two times and use a drive copy device looks like easier^^ and i get a 1:1 copy
You can do that but I just checked Syncthing is not the right tool for that as it syncs two disks over the network, for local sync of two dirs you may want need to use a tool like rsync (linux command line tool).
Raid would be the best
Yes, and only if you are talking about system running on one disk and plus two disks under raid for data. That we will support eventually. Plus some form of notification of failures (https://en.wikipedia.org/wiki/S.M.A.R.T.)
If you want to have just two disks and run Syncloud system on them then you have to create raid before “installing” (copy disk image, there is no installer) Syncloud.
I do understand that ideally you want all of that with zero configure, like a device has two disks out of the box and tells you when to buy a replacement one. Also if you get a second device they magically find each other and ask you to allow them to backup each other. Eventually we will get there if and when we get more resources.