I was doing a bit of research to see if this was possible. I wanted to install the entirety of Ubuntu (desktop), including /boot and everything on LVM on top of software RAID1.
Hopefully the above shows what I want to do (ignoring lack of fs). I am currently unsure whether this is possible because of old documentation that seems to present conflicting information. I don't really care if it isn't possible but I am very interested.
sda | sdb sdc | sdd
| | | |
/boot / /swap /home