If you want to use RAID (and probably LVM) use the non-live server image (even for desktops) and save yourself a lot of hassle:
http://cdimage.ubuntu.com/releases/18.04.2/release/ubuntu-18.04.2-server-amd64.iso
I could not get RAID1 to work for a desktop install any other way. I didn't have similar problems with my last desktop, built initially with Ubuntu 11.04 and ubiquity 2.6.10.
If you want to use RAID (and probably LVM) use the non-live server image (even for desktops) and save yourself a lot of hassle:
http:// cdimage. ubuntu. com/releases/ 18.04.2/ release/ ubuntu- 18.04.2- server- amd64.iso
I could not get RAID1 to work for a desktop install any other way. I didn't have similar problems with my last desktop, built initially with Ubuntu 11.04 and ubiquity 2.6.10.