I installed the mainline kernel from http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.4-precise/ and compiled the btrfs tools from git://git.kernel.org/pub/scm/linux/kernel/git/mason/btrfs-progs.git.
Then, I could remove the second drive after converting raid1 back to raid0:
% ./btrfs balance start --force -mconvert=raid0 /
I installed the mainline kernel from http:// kernel. ubuntu. com/~kernel- ppa/mainline/ v3.4-precise/ and compiled the btrfs tools from git://git. kernel. org/pub/ scm/linux/ kernel/ git/mason/ btrfs-progs. git.
Then, I could remove the second drive after converting raid1 back to raid0:
% ./btrfs balance start --force -mconvert=raid0 /