def save_diskspace(fname, reason, config):
    """Overwrite a file in place with a short message to save disk.

    This keeps files as a sanity check on processes working, but saves
    disk by replacing them with a short message.
    """
    if config["algorithm"].get("save_diskspace", False):
        for ext in ["", ".bai"]:
            if os.path.exists(fname + ext):
                with open(fname + ext, "w") as out_handle:
                    out_handle.write("File removed to save disk space: %s" % reason)