def get_default_volume_size(dataset_backend_configuration):
    # Ideally, the minimum allocatable size (and perhaps the default volume
    # size) would be something known by an object that represents the dataset
    # backend. Unfortunately:
    #  1. There is no such object
    #  2. There is existing confusion in the code around 'openstack' and
    #     'rackspace'
    #
    # Here, we special-case Rackspace (presumably) because it has a minimum
    # allocatable size that is different from other Openstack backends.
    #
    # FLOC-2584 also discusses this.
    default_volume_size = GiB(1)
    if dataset_backend_configuration.get('auth_plugin') == 'rackspace':
        default_volume_size = RACKSPACE_MINIMUM_VOLUME_SIZE
    return int(default_volume_size.to_Byte().value)
Calculate the default volume size for the given dataset backend
dataset/ETHPy150Open ClusterHQ/flocker/admin/acceptance.py/get_default_volume_size