def snapshot_pool(service, pool_name, snapshot_name):
    """
    Snapshots a RADOS pool in ceph.
    :param service: six.string_types. The Ceph user name to run the command under
    :param pool_name: six.string_types
    :param snapshot_name: six.string_types
    :return: None.  Can raise CalledProcessError
    """
    cmd = ['ceph', '--id', service, 'osd', 'pool', 'mksnap', pool_name, snapshot_name]
    try:
        check_call(cmd)
    except CalledProcessError:
        raise