#!/bin/sh

# replace with whatever your additional device is called
# /dev/sda should be where your CoreOS install lives right now
newdevice="/dev/sdb"
# 0 or 1
raidtype="0"

# make sure to download the single-partition.layout file as well

# create single primary partition on $newdevice (you could also run fdisk interactively, choose p command and use defaults it suggests)
sudo sfdisk $newdevice < single-partition.layout

# mount current root; I suppose /dev/sda9 would work as well?
sudo mount /dev/disk/by-label/ROOT /mnt

# add btrfs device
sudo btrfs device add /dev/sdb1 /mnt

# convert to raid of given type; don't use -mconvert=raid0 but not sure if it's beneficial to add -mconvert=raid1 when making a RAID1 (I think it might be!)
sudo btrfs balance start -dconvert=raid$raidtype /mnt

# might take a bit, depending on how much data there is to copy over

# verify things have worked
sudo btrfs fi df /mnt
# should show something like...
#Data, RAID0: total=6.00GiB, used=303.25MiB
#System, DUP: total=8.00MiB, used=16.00KiB
#System, single: total=4.00MiB, used=0.00
#Metadata, DUP: total=108.06MiB, used=18.78MiB
#Metadata, single: total=8.00MiB, used=0.00
#unknown, single: total=16.00MiB, used=0.00

# clean up
sudo umount /mnt