protected static function _formatSize($bytes)
    {
        $exp    = 0;
        $value  = 0;
        $symbol = array('B', 'KB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB');

        if ($bytes > 0) {
            $exp   = floor(log($bytes) / log(1024));
            $value = ($bytes / pow(1024, floor($exp)));
        }

        return sprintf('%.2f ' . $symbol[$exp], $value);
    }