Ubuntu Grub RAID Issues
Grub Fails To Install on RAID Array
If grub fails to install on your RAID array in any version of Ubuntu, do NOT disable your BIOS RAID! The correct solution is at this blog entry. I'll summarize it below.
At the stage of the install where it is attempting to install GRUB it will detect as
/dev/mapper
This is incomplete! That's why the GRUB install fails.
You need the actual name of the RAID array to install to. So during that step, press ctrl+alt+F2 to drop to a busybox terminal, then enter
ls -l /dev/mapper
Pick out the name of your array from the list shown, then press ctrl+alt+F1 to switch back to the install (you can switch back and forth as much as you like with no problems) and enter it in the field as
/dev/mapper/{your array name}
Then GRUB installs perfectly and you're ready to go, with a proper BIOS RAID array intact.
System Won't Boot After Grub Failed to Install
If your system will no longer boot because you skipped installing or updating grub, you need to download an Ubuntu version that does support RAID, boot from the LIVE CD, drop to a terminal, and then run:
ls -l /dev/mapper
sudo grub-install /dev/mapper/{ARRAY_NAME_HERE}
Setting Up RAID Array During Ubuntu Install
If you are configuring a BIOS RAID array for the first time on Ubuntu, you should create a 1MB boot partition. Its partition type is "boot". If you do this, grub will always try to install there and will succeed every time without failing when upgrading or reinstalling grub.