Question

Has anyone written a Fast Algorithm that generates a LARGE dummy file in PHP, say 500MB-2GB?

Answer 1

If you don’t care about the file contents at all, you can just seek to any position and write something:

$f = fopen('largefile', 'wb');
fseek($f, 2 * 1000 * 1000 * 1000, SEEK_SET);
fwrite($f, 'after 2 GB');
fclose($f);

If the OS and filesystem support sparse files, the file will be really big, but not actually take more than a couple of bytes of disk space.