UEFI requires booting from a ESP which is most of the time formatted as vFAT. If I recall correctly BTRFS could have sub-volumes formatted as ext3/ext4 like the Logical Volume Manager (LVM). However, UEFI doesn't support booting from BTRFS. Most of the time the solution is simply to use three (or 2N + 1) disks, two for the RAID and one from which to boot. My main concern in this case is simple RAID1 mirroring. In this case though I can only use two disks. If the motherboard were using BIOS then I could simply mirror the boot partition.
I've heard that this issue (having to use an extra disk to boot from) is one motivation why people have switched to (freeBSD with) ZFS, although I might be recalling falsely.
In my case what I did is mirror an entire disk with a partition. Id est, the second disk had two partitions: one ESP, one btrfs partition. However, I'm assuming this is not how BTRFS-RAID1 is intending to be used. So my question is concretely:
- Will this configuration lead to corruption or other unintended consequences?
- What would a better solution be?