I have filed two doc bugs that are fairly easy to fix. GRUB will assemble and boot pretty much anything these days: md RAID 0, 1, 4, 5, 6; and in addition to ext[234], it understands FAT, NTFS, ZFS, HFS+, XFS and Btrfs. It'll even boot from Btrfs subvols, on a volume configured using data profile single, raid[0,1,10].

https://bugzilla.redhat.com/show_bug.cgi?id=887987
https://bugzilla.redhat.com/show_bug.cgi?id=888099


There are some limitations for how many devices GRUB may be able to find. It seems like 4 devices is a safe lowest common denominator (accounts for some Btrfs 5+ disk boot failures).

http://lists.gnu.org/archive/html/grub-devel/2013-01/msg00025.html


Chris Murphy