Nextcloud for me. I run my own home server, which is just a normal PC on a cheap UPS, on a residential internet connection with dynamic DNS. On that, Proxmox, and Nextcloud lives in there as an LXC container.
On my phone, the Nextcloud app is installed, and that takes care of the photo/video/downloaded file "cloud" sync, and DAVx5 takes care of calendar, contacts, todo. Nextcloud, with additional apps, can also do Kanban, multimedia notes.
I see your point, but from the perspective of the Android phone, this is already a backup. This is because if I lose the phone, I can restore the important parts of its state from the copy on the server - which is the definition of a backup, according to Wikipedia for example.
Now, of course, we can look at more stringent approaches to backing up data, which I already do, but for some reason I didn't elaborate on the original comment. My home server uses ZFS as storage, and I snapshot that from time to time, and I sync those snapshots to another, otherwise offline ZFS storage. The true 3-2-1 I still don't achieve, because both the online and the offline copies are at the same site, but I opted to take this risk.
>I see your point, but from the perspective of the Android phone, this is already a backup. This is because if I lose the phone, I can restore the important parts of its state from the copy on the server - which is the definition of a backup, according to Wikipedia for example.
I am not familiar enough with nextcloud but what happens if - excluding your home server setup - you modify a picture on your smartphone and overwrite it? I guess it is synchronized to the nextcloud server in modified form and replace the original file, right[1]? If so what if you were to realize you screwed up and should not have overwritten it? Hence the reason I am saying it is not exactly a backup.
[1] that would be the behavior I expect of a syncing mechanism, I use syncthing-fork myself for that.
Ah, right, then maybe I didn't see the point after all. Nextcloud handles this quite well though, I think, it will say, on the phone, that there is a conflict between the two versions of the file, and in case of images, it ever shows them side by side, and asks you what to do.
OK in that case that makes at least clearer for the user. Thanks.
Nextcloud has a first-party plugin that keeps a version history, which is very useful to enable to mitigate issues like this. That combined with the default behavior that deletions on devices only go to the trash on the server turns it into a real backup option.
Important to note: unless backups are implemented on the nextcloud server itself, this is sync, not backup.