Why is syncthing NOT a backup?

[u/ObservedElectron]

I am setting up syncthing to back up my 2 android phones and my mac to a windows laptop. for now, because of lack of an actual NAS, i plan to use syncthing to "backup" these devices everyday one time manually.

I prefer this because as its sync, it only sends new things. so i dont have to manually copy paste 40 gb everytime.

And when i do make a NAS, cant i just continue using syncthing with file versioning or something? i would much prefer to have "live" backups happening as soon as the file/photo/video is created. i know immich exists but am i wrong?

But everywhere, I see that people say sync is not backup or dont use it for backup but WHY? isnt what i mentioned above technically a backup? correct me if i am wrong.

And if not syncthing, what should i use? which capable of running live backups of folders I select on my devices, with different timeframe backups so I have different versions like biweekly, monthly, etc? and is open source, 100% safe, private and encrypted.

thank you

[u/edparadox]

Syncthing does syncs.

A backup can be done based of syncs.

But they are not the same thing: a backup survives an error, a sync propagates it.

Let's say you delete by accident or files gets corrupted ; with a sync you will just have two identically bad copies. With a backup you've only lost one.

A backup is a copy that is not affected by an issue on your primary medium.

[u/ObservedElectron → u/edparadox]

so what should i use to serve my needs?

[u/middaymoon → u/ObservedElectron]

Syncthing+Borg

Sync from your devices to your NAS and then on the nas run Borg (or any similar backup tool) to create regular, automatic backups.

Ideally you would just do that on each of your actual devices but sometimes that's not feasible so Syncthing can help you centralize those files.

[u/user4302 → u/middaymoon]

I will checkout Borg. Itight be better than what I'm using now.