freefilesync is also free & is an open source program
http://sourceforge.net/projects/freefilesync/
& has more/better features than synctoy
http://sourceforge.net/projects/free.../topic/3421064
http://www.makeuseof.com/tag/is-free...nctoy-windows/
it is very fast as it caches directory info somehow & can thus recheck a huge library & spot changes since last run in a couple of seconds