Installing on btrfs raid1 root fails (with /boot partition)

[Benjamin Tegge]

Similar to #1629576, but now with a boot partition after the Fedora Workstation installer told me that I do need a boot partition.

I created a mirrored btrfs volume in a VM for testing before installing:

sudo mkfs.btrfs -f -m raid1 -d raid1 /dev/sda4 /dev/sdb4

I then tried to install with ubiquity to one of the btrfs partitions (according to http://wiki.ubuntuusers.de/Installieren_auf_Btrfs-Dateisystem/ this is okay).

Output of lsblk after the installer crashed (a btrfs install is supposed to create necessary subvolumes):

ubuntu@ubuntu:~$ lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 10G 0 disk
├─sda1 8:1 0 100M 0 part /target/boot/efi
├─sda2 8:2 0 500M 0 part /target/boot
├─sda3 8:3 0 999M 0 part [SWAP]
└─sda4 8:4 0 8.4G 0 part /target/home
sdb 8:16 0 10G 0 disk
├─sdb1 8:17 0 100M 0 part
├─sdb2 8:18 0 500M 0 part
├─sdb3 8:19 0 999M 0 part [SWAP]
└─sdb4 8:20 0 8.4G 0 part
sr0 11:0 1 1.4G 0 rom /cdrom
loop0 7:0 0 1.4G 1 loop /rofs

ubuntu@ubuntu:~$ sudo btrfs filesystem show
Label: none uuid: f45656e6-5d73-45a6-aaa5-37b0af54ece8
 Total devices 2 FS bytes used 3.75GiB
 devid 1 size 8.44GiB used 5.01GiB path /dev/sda4
 devid 2 size 8.44GiB used 5.01GiB path /dev/sdb4

ubuntu@ubuntu:~$ sudo btrfs subvolume list /target/
ID 258 gen 292 top level 5 path @
ID 259 gen 75 top level 5 path @home

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubiquity 2.21.63.2
ProcVersionSignature: Ubuntu 4.4.0-31.50-generic 4.4.13
Uname: Linux 4.4.0-31-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.1
Architecture: amd64
CasperVersion: 1.376
Date: Sun Oct 2 22:12:11 2016
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz.efi file=/cdrom/preseed/ubuntu.seed boot=casper quiet splash ---
LiveMediaBuild: Ubuntu 16.04.1 LTS "Xenial Xerus" - Release amd64 (20160719)
ProcEnviron:
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)