def config_fallocate_value(reserve_value):
    """
    Returns fallocate reserve_value as an int or float.
    Returns is_percent as a boolean.
    Returns a ValueError on invalid fallocate value.
    """
    try:
        if str(reserve_value[-1:]) == '%':
            reserve_value = float(reserve_value[:-1])
            is_percent = True
        else:
            reserve_value = int(reserve_value)
            is_percent = False
    except ValueError:
        raise ValueError(
            'Error: %s is an invalid value for fallocate_reserve.' %
            reserve_value)
    return reserve_value, is_percent
