Don't confuse backups with syncing. Although syncthing has a recycle bin to recover deleted and overwritten files, you shouldn't rely on it for guarding against accidental deletion, file corruption, or ransomware. You want something that will allow you to restore files from a point in time. There's lots of proper backup tools for this. Borg, Restic, etc. Each has pros and cons. Make sure you test recovery. Also 3-2-1 is 3 copies of data, on at least 2 different systems, and 1 off site.

As others have said, sync isn't backup - if you inadvertently delete something then it will get deleted everywhere.

I've been using borgmatic (config interface for borg) for many years.

A long while ago I switched to catch and release for media. Curating a large collection just took too much effort, and backing it up was too impractical. Like you probably have 200gb of movies, 20gb of photos, and 20mb of personal documents. These categories have different risk profiles - for me an offsite air gapped backup of movies would be excessive, but personal documents absolutely isn't. It's just an important consideration when designing a backup system.

That said, 200gb isn't that much, and restic / borg will de-duplicate your archives anyway. Just something to keep in mind.

A low powered PC in someone else's apartment satisfies the second location requirement. Will DNS be a problem?

An alternative is to get 2x external drives. Keep one in your house and update it whenever, then take it to your sister's whenever you visit and swap it with the one left there.

Duplicati or Borg for backups. Guis exist for borg as well.

That sounds fine. I would only say don't use Syncthing to actually make your backups. My preference and recommendation is restic, possibly combined with the helper utility autorestic.

Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:

5 acronyms in this thread; the most compressed thread commented on today has 6 acronyms.

[Thread #68 for this comm, first seen 7th Feb 2026, 04:40] [FAQ] [Full list] [Contact] [Source code]

If you're going for reliability, and you just want things to be simple, you probably just want to spend the money on two cheap NAS boxes, honestly. There are some caveats that come with RPi's, and you're unfamiliar it's: 1) going to cost about the same, 2) be simpler to manage and upgrade, and 3) be easier to repair disk columes when the time comes.

Even if you're just looking to make these redundant to each other, just make it simple and easy.