“1. Pick an external storage, which you want to move your persistent data to.
6. …your data will from now on be written to the external disk.”
What do you mean by “your data will from now on be written to the external disk”? If it means just moving of /srv, I would welcome if it was written in Foris in a clearer way. I.e. what you will move to a new location for us and what we have to (or should) move manually after that. You write about “Nextcloud, LXC or other IO intensive applications” but it seems that Storage plugin will move /srv only. That doc page seems to me a little bit confusing.