Not sure if the following scenarios should be mentioned in this bug or new bugs should be created (both similar but unique tracebacks included below in respective order):

1. A volume with that name already exists (perhaps on a different disk)
2. A volume group is assumed to exist when it does not

config-changed   Physical volume "/dev/loop0" successfully created
config-changed   A volume group called cinder-volumes already exists.
config-changed Traceback (most recent call last):
config-changed   File "/var/lib/juju/agents/unit-cinder-0/charm/hooks/config-changed", line 519, in <module>
config-changed     hooks.execute(sys.argv)
config-changed   File "/var/lib/juju/agents/unit-cinder-0/charm/hooks/charmhelpers/core/hookenv.py", line 557, in execute
config-changed     self._hooks[hook_name]()
config-changed   File "/var/lib/juju/agents/unit-cinder-0/charm/hooks/charmhelpers/core/host.py", line 312, in wrapped_f
config-changed     f(*args, **kwargs)
config-changed   File "/var/lib/juju/agents/unit-cinder-0/charm/hooks/config-changed", line 131, in config_changed
config-changed     conf['remove-missing'])
config-changed   File "/var/lib/juju/agents/unit-cinder-0/charm/hooks/cinder_utils.py", line 372, in configure_lvm_storage
config-changed     create_lvm_volume_group(volume_group, new_devices[0])
config-changed   File "/var/lib/juju/agents/unit-cinder-0/charm/hooks/charmhelpers/contrib/storage/linux/lvm.py", line 105, in create_lvm_volume_group
config-changed     check_call(['vgcreate', volume_group, block_device])
config-changed   File "/usr/lib/python2.7/subprocess.py", line 511, in check_call
config-changed     raise CalledProcessError(retcode, cmd)
config-changed subprocess.CalledProcessError: Command '['vgcreate', u'cinder-volumes', '/dev/loop0']' returned non-zero exit status 5


config-changed   Volume group "cinder-volumes" not found
config-changed Traceback (most recent call last):
config-changed   File "/var/lib/juju/agents/unit-cinder-0/charm/hooks/config-changed", line 519, in <module>
config-changed     hooks.execute(sys.argv)
config-changed   File "/var/lib/juju/agents/unit-cinder-0/charm/hooks/charmhelpers/core/hookenv.py", line 557, in execute
config-changed     self._hooks[hook_name]()
config-changed   File "/var/lib/juju/agents/unit-cinder-0/charm/hooks/charmhelpers/core/host.py", line 312, in wrapped_f
config-changed     f(*args, **kwargs)
config-changed   File "/var/lib/juju/agents/unit-cinder-0/charm/hooks/config-changed", line 131, in config_changed
config-changed     conf['remove-missing'])
config-changed   File "/var/lib/juju/agents/unit-cinder-0/charm/hooks/cinder_utils.py", line 377, in configure_lvm_storage
config-changed     reduce_lvm_volume_group_missing(volume_group)
config-changed   File "/var/lib/juju/agents/unit-cinder-0/charm/hooks/cinder_utils.py", line 313, in reduce_lvm_volume_group_missing
config-changed     subprocess.check_call(['vgreduce', '--removemissing', volume_group])
config-changed   File "/usr/lib/python2.7/subprocess.py", line 511, in check_call
config-changed     raise CalledProcessError(retcode, cmd)
config-changed subprocess.CalledProcessError: Command '['vgreduce', '--removemissing', u'cinder-volumes']' returned non-zero exit status 5