OFF TOPIC
I’m confused 
(for a change)
I’m not looking to have file-based or LVM or anything, I just want to have a robust stable Qubes running, and using RAID1 in case I have one that fails.
Each is 2TB, so I don’t need more room (for now), and RAID0 would defeat the purpose.
Qubes doesn’t see my bios RAID1, so I’ve been told to use soft.RAID1 instead.
Automatic partition is a no-go as it doesn’t ask for user requirement, and go straight to full disk, therefore I wouldn’t have my sysrun in the “cheap” one (the 256GB) and the system in mirror.
I’ve spent 3 years on that setup (don’t laugh, on a very dilettante way !)
PS: I’m just waiting for Qubes-OS 7.0 native ZFS 