Fast large folder comparison utility on Mac (maybe Windows)
Solution 1:
Try out Unison. Free/open source. Uses rsync algorithm for sync, so only changed bits move. Handles 2-way sync. Fast.
Unison is a file-synchronization tool for Unix and Windows. It allows two replicas of a collection of files and directories to be stored on different hosts (or different disks on the same host), modified separately, and then brought up to date by propagating the changes in each replica to the other.
Solution 2:
Have you look at the free utility SyncToy 2.1 I use it to keep backups to USB drive and it may meet your needs. I hope this helps.
Solution 3:
A very old trick : for every file, make another file adding the suffix .crc ... with the crc of its pal.
Now, you
- make the crc trick for every new incoming file
- you just compare the crc files : blazing fast, also over slow network links
Under linux there is the standard utility cksum. Similar tools are wide-spread, from the ancient time of BBS over 9600 baud tel.co. links :-)