public function formatUsage($bytes, $maxbytes)
    {
        if (!is_numeric($maxbytes) || $maxbytes < 1) {
            return '(undefined)';
        }

        $out = round($bytes / $maxbytes, 3) . "% (";
        $out .= round($bytes / 1024 / 1024, 2) . 'MB of ';
        $out .= round($maxbytes / 1024 / 1024, 2) . 'MB)';

        return $out;
    }