function generate_file($file_name, $size_in_bytes)
{
   $data = str_repeat(rand(0,9), $size_in_bytes);
   file_put_contents($file_name, $data); //writes $data in a file
}

fsutil file createnew d:filepathfilename.txt 1048576

dd if=/dev/zero of=filepath/filename.txt bs=10000000 count=1

function file_rand($filename, $filesize) {
    if ($h = fopen($filename, 'w')) {
        if ($filesize > 1024) {
            for ($i = 0; $i < floor($filesize / 1024); $i++) {
                fwrite($h, bin2hex(openssl_random_pseudo_bytes(511)) . PHP_EOL);
            }
            $filesize = $filesize - (1024 * $i);
        }
        $mod = $filesize % 2;
        fwrite($h, bin2hex(openssl_random_pseudo_bytes(($filesize - $mod) / 2)));
        if ($mod) {
            fwrite($h, substr(uniqid(), 0, 1));
        }
        fclose($h);
        umask(0000);
        chmod($filename, 0644);
    }
}

$data = '';
for ($byteSize-- >= 0) {
    $data .= chr(rand(0,255));
}

function CreatFileDummy($file_name,$size = 90294967296 ) {
// 32bits 4 294 967 296 bytes MAX Size
    $f = fopen('dummy/'.$file_name, 'wb');
    if($size >= 1000000000)  {
        $z = ($size / 1000000000);
        if (is_float($z))  {
            $z = round($z,0);
            fseek($f, ( $size - ($z * 1000000000) -1 ), SEEK_END);
            fwrite($f, "");
        }
        while(--$z > -1) {
            fseek($f, 999999999, SEEK_END);
            fwrite($f, "");
        }
    }
    else {
        fseek($f, $size - 1, SEEK_END);
        fwrite($f, "");
    }
    fclose($f);

return true;
}