[lubuntu] lxd storage pool

Hi,
I'm installing lxd in my home lab in btrfs
root in one btrfs file system and I mounted another btrfs file system sub-volume to /var/lib/lxd

when I try to create new VM complain with this error
# lxc launch ubuntu:14.04 my-ubuntu
error: No storage pool found. Please create a new storage pool.

# lxc storage list
+------+--------+--------+---------+
| NAME | DRIVER | SOURCE | USED BY |
+------+--------+--------+---------+


I assume problem is default storage pool not defined.
I try to create a pool with following command
lxc storage create default btrfs source=/var/lib/lxd

But failed since trying create another sub-volume to /var/lib/lxd.

How could I edit default storage pool to add /var/lib/lxd?

Thank you,