This isn’t true if you have a bootloader on each drive, which, I think, is what the we’re talking about.
It’s called “adsomeWm”… highly un-customizinle.
I’d recommend the following, which is what I did
I’d highly suggest, not to put everything in one box. Been there, nothing but struggles.
Lol… 90% of the folks there probably don’t even know what that means.
Haven’t done it myself, but his might help you for further research
iptables
https://unix.stackexchange.com/questions/264589/traffic-of-specific-program-through-vpn
network interfaces
https://unix.stackexchange.com/questions/234583/routing-on-per-application-basis