'Create a dataset, then wait for convergence.'

def run(self):

    d = self.control_service.create_dataset(primary=self.primary.uuid, maximum_size=self.volume_size, dataset_id=self.dataset_id)
    def loop_until_converged(expected):
        return loop_until(self.reactor, partial(self._converged, expected))
    d.addCallback(loop_until_converged)
    return d
