I wrote a simple backup script which puts all files in his folder (and all of the sub-folders) in one TAR archive...
(It's classic TAR format not USTAR, so filename and path to it can't be longer then 99 chars)
<?php
/***********************************************************
 *   Title:  Classic-TAR based backup script v0.0.1-dev
  **********************************************************/

Class Tar_by_Vladson {
    var $tar_file;
    var $fp;
    function Tar_by_Vladson($tar_file='backup.tar') {
        $this->tar_file = $tar_file;
        $this->fp = fopen($this->tar_file, "wb");
        $tree = $this->build_tree();
        $this->process_tree($tree);
        fputs($this->fp, pack("a512", ""));
        fclose($this->fp);
    }
    function build_tree($dir='.'){
        $handle = opendir($dir);
        while(false !== ($readdir = readdir($handle))){
            if($readdir != '.' && $readdir != '..'){
                $path = $dir.'/'.$readdir;
                if (is_file($path)) {
                    $output[] = substr($path, 2, strlen($path));
                } elseif (is_dir($path)) {
                    $output[] = substr($path, 2, strlen($path)).'/';
                    $output = array_merge($output, $this->build_tree($path));
                }
            }
        }
        closedir($handle);
        return $output;
    }
    function process_tree($tree) {
        foreach( $tree as $pathfile ) {
            if (substr($pathfile, -1, 1) == '/') {
                fputs($this->fp, $this->build_header($pathfile));
            } elseif ($pathfile != $this->tar_file) {
                $filesize = filesize($pathfile);
                $block_len = 512*ceil($filesize/512)-$filesize;
                fputs($this->fp, $this->build_header($pathfile));
                fputs($this->fp, file_get_contents($pathfile));
                fputs($this->fp, pack("a".$block_len, ""));
            }
        }
        return true;
    }
    function build_header($pathfile) {
        if ( strlen($pathfile) > 99 ) die('Error');
        $info = stat($pathfile);
        if ( is_dir($pathfile) ) $info[7] = 0;
        $header = pack("a100a8a8a8a12A12a8a1a100a255",
            $pathfile,
            sprintf("%6s ", decoct($info[2])),
            sprintf("%6s ", decoct($info[4])),
            sprintf("%6s ", decoct($info[5])),
            sprintf("%11s ",decoct($info[7])),
            sprintf("%11s", decoct($info[9])),
            sprintf("%8s", " "),
            (is_dir($pathfile) ? "5" : "0"),
            "",
            ""
            );
        clearstatcache();
        $checksum = 0;
        for ($i=0; $i<512; $i++) {
            $checksum += ord(substr($header,$i,1));
        }
        $checksum_data = pack(
            "a8", sprintf("%6s ", decoct($checksum))
            );
        for ($i=0, $j=148; $i<7; $i++, $j++)
            $header[$j] = $checksum_data[$i];
        return $header;
    }
}

header('Content-type: text/plain');
$start_time = array_sum(explode(chr(32), microtime()));
$tar = & new Tar_by_Vladson();
$finish_time = array_sum(explode(chr(32), microtime()));
printf("The time taken: %f seconds", ($finish_time - $start_time));
?>