def get_size_info(api, volume):
    backing_file = api._root_path.descendant(
        ['unattached', _backing_file_name(volume)]
    )
    # Get actual number of 512 byte blocks used by the file.  See
    # http://stackoverflow.com/a/3212102
    backing_file.restat()
    actual = backing_file.statinfo.st_blocks * 512
    reported = backing_file.getsize()
    return _SizeInfo(actual=actual, reported=reported)
Retrieve information about the size of the backing file for the given
dataset/ETHPy150Open ClusterHQ/flocker/flocker/node/agents/test/test_blockdevice.py/get_size_info