':param device: name of target device
:param partition: partition name
:param suffixes: a list of suffix directories to be recalculated
:param policy: the StoragePolicy instance
:returns: a dictionary that maps suffix directories'

def get_hashes(self, device, partition, suffixes, policy):

    dev_path = self.get_dev_path(device)
    if (not dev_path):
        raise DiskFileDeviceUnavailable()
    partition_path = get_part_path(dev_path, policy, partition)
    if (not os.path.exists(partition_path)):
        mkdirs(partition_path)
    (_junk, hashes) = tpool_reraise(self._get_hashes, device, partition, policy, recalculate=suffixes)
    return hashes
