public function setMaxSize($max_size)
    {
        if (is_numeric($max_size)) {
            $this->max_size = $max_size;
        } else {
            $this->max_size = Util::humanReadableToBytes($max_size);
        }

        if ($this->max_size < 0 || $this->max_size == null) {
            throw new \Exception('invalid max_size value');
        }

    }