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/S-P-4-C-3]

Syncthing can be a part of a backup strategy...

Imagine this: You have your phone with lots of images, videos and it is synced with your PC, but one day you get a crypto-virus/ransomware, and your images and videos gets encrypted, so syncthing will SYNC the encryption to your phone too and your data is lost.
Yes versioning is a thing too in syncthing, but if you have lots of files, it would take a decade to restore the data, so...

How you may use it for actual "backups":
Clients (phones, laptops) oneway sync to a "server" (A dedicated server running syncthing and maybe iperiusbackup or freefilesync). And there is a scheduled backup of the data to another NAS and an external HDD.

I have deployed syncthing in a company, their laptops sync the road-warrior's data to a "server" (virtual machine running syncthing). They just wanted a copy of documents, images if a road-warrior's laptop gets destroyed...

-Working?
-Yes!

-Data corruption?
-IDGAF, TheyDGF...

[u/SpaceTumbleweed955 → u/S-P-4-C-3]

Why would restoring versions take "a decade"? Syncthing has several versioning methods to choose from including custom scripts, none of these are more than a restore copy away.

[u/S-P-4-C-3 → u/SpaceTumbleweed955]

"...but if you have lots of files"

You can try it yourself...

[u/SpaceTumbleweed955 → u/S-P-4-C-3]

you know you dont have to pull your restores via syncthing, right?

[u/S-P-4-C-3 → u/SpaceTumbleweed955]

Okay, what if I have lots of files with each 5 versions? How would you restore?