Performing a major version upgrade is never pleasant. I've been using ProxmoxVE for about ten years now though, and it's consistently done a fantastic job. Since it's based on Debian, all the upgrades are done with a simple
apt update && apt upgrade, with a variety of steps in the middle to point to new repositories, etc. Nothing out of the ordinary, nothing scary.
So I've got two servers - one is an old one, with only a couple testing VM's residing on it. I go ahead and work through the 5 …