I am sure I saw a free program in Web User a few months ago that synchronised folders on different hard disks. I have looked through loads of old copies but I can't find it.
No idea if this is the specific one that you are trying to recall, but the one I use without any problems is Syncback http://www.2brightsparks.com/syncback/. It's freeware and has been trouble free in the months that I've used it.