Comment 7 for bug 1696184

confirmed. a true dup of #880766 from 2011. Today is 2017 and installing ubuntu on software raid is still unsupported scenario. this is ubuntu...

workaround:

1. install w/o the bootloader (undocumented switch!)
sudo ubiquity -b

2. chroot into target system, install mdadm, switch grub-pc to grub-efi, profit.

root@ubuntu-gnome:/root/tsta# mount /dev/mapper/root_crypt /tgt
root@ubuntu-gnome:/root/tsta# mount -o bind /dev /tgt/dev
root@ubuntu-gnome:/root/tsta# mount -o bind /dev/pts /tgt/dev/pts
root@ubuntu-gnome:/root/tsta# mount -o bind /sys /tgt/sys
root@ubuntu-gnome:/root/tsta# mount -o bind /proc /tgt/proc
root@ubuntu-gnome:/root/tsta# cat /etc/resolv.conf > /tgt/etc/resolv.conf
root@ubuntu-gnome:/root/tsta# mount /dev/md0 /tgt/boot
root@ubuntu-gnome:/root/tsta# chroot /tgt
root@ubuntu-gnome:/# mount /dev/sda1 /boot/efi

root@ubuntu-gnome:/# apt-get install mdadm
Reading package lists... Done
Building dependency tree
Reading state information... Done
Suggested packages:
  default-mta | mail-transport-agent
The following NEW packages will be installed:
  mdadm
0 upgraded, 1 newly installed, 0 to remove and 194 not upgraded.
Need to get 393 kB of archives.
After this operation, 1,203 kB of additional disk space will be used.
Get:1 http://us.archive.ubuntu.com/ubuntu xenial-updates/main amd64 mdadm amd64 3.3-2ubuntu7.2 [393 kB]
Fetched 393 kB in 0s (778 kB/s)
Preconfiguring packages ...
Selecting previously unselected package mdadm.
(Reading database ... 188668 files and directories currently installed.)
Preparing to unpack .../mdadm_3.3-2ubuntu7.2_amd64.deb ...
Unpacking mdadm (3.3-2ubuntu7.2) ...
Processing triggers for systemd (229-4ubuntu16) ...
Processing triggers for ureadahead (0.100.0-19) ...
Processing triggers for man-db (2.7.5-1) ...
Setting up mdadm (3.3-2ubuntu7.2) ...
Generating mdadm.conf... done.
update-initramfs: deferring update (trigger activated)
/usr/sbin/grub-mkconfig: 250: /usr/sbin/grub-mkconfig: cannot create /boot/grub/grub.cfg.new: Directory nonexistent
Running in chroot, ignoring request.
update-rc.d: warning: start and stop actions are no longer supported; falling back to defaults
Processing triggers for systemd (229-4ubuntu16) ...
Processing triggers for ureadahead (0.100.0-19) ...
Processing triggers for initramfs-tools (0.122ubuntu8.8) ...
update-initramfs: Generating /boot/initrd.img-4.8.0-54-generic

root@ubuntu-gnome:/# grub-install /dev/sda
Installing for i386-pc platform.
grub-install: warning: this GPT partition label contains no BIOS Boot Partition; embedding won't be possible.
grub-install: error: embedding is not possible, but this is required for RAID and LVM install.

root@ubuntu-gnome:/# apt-get install grub-efi
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following additional packages will be installed:
  grub-common grub-efi-amd64 grub-efi-amd64-bin grub-pc-bin grub2-common
Suggested packages:
  multiboot-doc grub-emu xorriso desktop-base
The following packages will be REMOVED:
  grub-gfxpayload-lists grub-pc
The following NEW packages will be installed:
  grub-efi grub-efi-amd64 grub-efi-amd64-bin
The following packages will be upgraded:
  grub-common grub-pc-bin grub2-common
3 upgraded, 3 newly installed, 2 to remove and 190 not upgraded.
Need to get 3,831 kB of archives.
After this operation, 2,447 kB of additional disk space will be used.
Do you want to continue? [Y/n]
Get:1 http://us.archive.ubuntu.com/ubuntu xenial-updates/main amd64 grub2-common amd64 2.02~beta2-36ubuntu3.9 [510 kB]
Get:2 http://us.archive.ubuntu.com/ubuntu xenial-updates/main amd64 grub-pc-bin amd64 2.02~beta2-36ubuntu3.9 [888 kB]
Get:3 http://us.archive.ubuntu.com/ubuntu xenial-updates/main amd64 grub-common amd64 2.02~beta2-36ubuntu3.9 [1,706 kB]
Get:4 http://us.archive.ubuntu.com/ubuntu xenial-updates/main amd64 grub-efi-amd64-bin amd64 2.02~beta2-36ubuntu3.9 [658 kB]
Get:5 http://us.archive.ubuntu.com/ubuntu xenial-updates/main amd64 grub-efi-amd64 amd64 2.02~beta2-36ubuntu3.9 [65.8 kB]
Get:6 http://us.archive.ubuntu.com/ubuntu xenial-updates/main amd64 grub-efi amd64 2.02~beta2-36ubuntu3.9 [2,538 B]
Fetched 3,831 kB in 2s (1,757 kB/s)
Preconfiguring packages ...
(Reading database ... 188735 files and directories currently installed.)
Removing grub-gfxpayload-lists (0.7) ...
Removing grub-pc (2.02~beta2-36ubuntu3.7) ...
Processing triggers for man-db (2.7.5-1) ...
(Reading database ... 188715 files and directories currently installed.)
Preparing to unpack .../grub2-common_2.02~beta2-36ubuntu3.9_amd64.deb ...
Unpacking grub2-common (2.02~beta2-36ubuntu3.9) over (2.02~beta2-36ubuntu3.7) ...
Preparing to unpack .../grub-pc-bin_2.02~beta2-36ubuntu3.9_amd64.deb ...
Unpacking grub-pc-bin (2.02~beta2-36ubuntu3.9) over (2.02~beta2-36ubuntu3.7) ...
Preparing to unpack .../grub-common_2.02~beta2-36ubuntu3.9_amd64.deb ...
Running in chroot, ignoring request.
Unpacking grub-common (2.02~beta2-36ubuntu3.9) over (2.02~beta2-36ubuntu3.7) ...
Selecting previously unselected package grub-efi-amd64-bin.
Preparing to unpack .../grub-efi-amd64-bin_2.02~beta2-36ubuntu3.9_amd64.deb ...
Unpacking grub-efi-amd64-bin (2.02~beta2-36ubuntu3.9) ...
Selecting previously unselected package grub-efi-amd64.
Preparing to unpack .../grub-efi-amd64_2.02~beta2-36ubuntu3.9_amd64.deb ...
Unpacking grub-efi-amd64 (2.02~beta2-36ubuntu3.9) ...
Selecting previously unselected package grub-efi.
Preparing to unpack .../grub-efi_2.02~beta2-36ubuntu3.9_amd64.deb ...
Unpacking grub-efi (2.02~beta2-36ubuntu3.9) ...
Processing triggers for install-info (6.1.0.dfsg.1-5) ...
Processing triggers for man-db (2.7.5-1) ...
Processing triggers for systemd (229-4ubuntu16) ...
Processing triggers for ureadahead (0.100.0-19) ...
Setting up grub-common (2.02~beta2-36ubuntu3.9) ...
Installing new version of config file /etc/grub.d/10_linux ...
update-rc.d: warning: start and stop actions are no longer supported; falling back to defaults
Running in chroot, ignoring request.
Setting up grub2-common (2.02~beta2-36ubuntu3.9) ...
Setting up grub-pc-bin (2.02~beta2-36ubuntu3.9) ...
Setting up grub-efi-amd64-bin (2.02~beta2-36ubuntu3.9) ...
Setting up grub-efi-amd64 (2.02~beta2-36ubuntu3.9) ...
Setting up grub-efi (2.02~beta2-36ubuntu3.9) ...
root@ubuntu-gnome:/# nano /etc/default/grub
root@ubuntu-gnome:/# update-grub
Generating grub configuration file ...
Warning: Setting GRUB_TIMEOUT to a non-zero value when GRUB_HIDDEN_TIMEOUT is set is no longer supported.
Found linux image: /boot/vmlinuz-4.8.0-54-generic
Found initrd image: /boot/initrd.img-4.8.0-54-generic
Found linux image: /boot/vmlinuz-4.8.0-36-generic
Found initrd image: /boot/initrd.img-4.8.0-36-generic
Adding boot menu entry for EFI firmware configuration
done

root@ubuntu-gnome:/# grub-install /dev/sda
Installing for x86_64-efi platform.
Installation finished. No error reported.