public function backup($is = true)
    {
        $is = (bool) $is;
        if ($this->backup === $is) {
            return $this;
        }
        $this->backup = $is;
        if ($this->backup) {
            $this->task->appendToBackupDrivers($this);
        } else {
            $this->task->removeFromBackupDrivers($this);
        }

        return $this;
    }