UPDATE I had to learn it the hard way… Just don’t do what I did and get yourself an HBA controller right away!
Otherwise you will run into (performance) problems sooner or later.
I was in the situation to install Proxmox on a second hand HP DL380 Gen8 Server with a P420i RAID controller.
Since Proxmox supports installation to ZFS out of the box I wanted to make use of that.
Note as of October 2019 The native ZFS encryption introduced in version 0.8 is working quite fine and you can use it for a root file system. With this in mind this guide is probably a bit outdated.
This blog entry is my personal documentation. If it helps others even better. I will try to keep it as up to date as possible. What helped me when I tried this the first time was the github gist by codedreality.