'Serialize this RingData instance to disk.
:param filename: File into which this instance should be serialized.
:param mtime: time used to override mtime for gzip, default or None
if the caller wants to include time'

def save(self, filename, mtime=1300507380.0):

    tempf = NamedTemporaryFile(dir='.', prefix=filename, delete=False)
    gz_file = GzipFile(filename, mode='wb', fileobj=tempf, mtime=mtime)
    self.serialize_v1(gz_file)
    gz_file.close()
    tempf.flush()
    os.fsync(tempf.fileno())
    tempf.close()
    os.chmod(tempf.name, 420)
    os.rename(tempf.name, filename)
