I use robocopy to back up my music collection to my D-Link DNS-321. I use the /xo switch so only new and modified files would be copied – like so:
However, it was taking forever because every file was considered “NEWER” than the existing backup copy. At first, I thought my music program (Media Monkey on Windows) was updating the mp3 tags or touching the files. That turned out to not be the case.
Instead, the issue was a difference in precision between timestamps on my laptop (Windows XP) and the DNS-321 (Linux/Samba).
The solution? The /fft switch: