To make full advantage from de-duplication it would be cool to backup several PCs / servers to the same repo. I didn’t find anything about this in the docs.
I would expect that this is possible, but I prefer to ask to be really sure: Is kopia concurrency-safe when accessing (and especially writing to) a shared repository? Is it required to use the kopia server? Or can several clients connect and update a shared repository at the same time without interfering?
Yes, it is possible to backup multiple machines to the same repo, and Kopia will deduplicate the whole repo. You do not need to use Kopia server. Just connect each machine to the same repo as normal and Kopia will handle the rest. See Features | Kopia
Ah, right, thanks. And this implies that the access to the repo is concurrency-safe i.e. if clients access the repo at the same time, they will coordinate themselves … somehow?
I don’t know the fine details of how it works under the hood (but you can always look at the source code if you are interested!). But, yes, Kopia is designed to work with multiple computers concurrently accessing a repo.