def _get_vdi_other_config(disk_type, instance=None):
    """Return metadata to store in VDI's other_config attribute.

    `nova_instance_uuid` is used to associate a VDI with a particular instance
    so that, if it becomes orphaned from an unclean shutdown of a
    compute-worker, we can safely detach it.
    """
    other_config = {'nova_disk_type': disk_type}
    if instance:
        other_config['nova_instance_uuid'] = instance['uuid']
    return other_config
