Vista - A more efficient way to copy files?

Today I use RoboCopy with the /Mir switch in Vista to make a mirror copy of
a data drive I have that contains a lot of multi-gigabyte video files. I've
recently started tagging them all, and find that I am tagging things with
all kind of different things. Problem is, tagging the file updates the
datestamp, and Robocopy thinks it's a more current file, so it copies the
ENTIRE multi-gigabyte file to the mirrored drive every time I update a tag.

Is their a better tool to use than Robocopy for this purpose...one that's
able to just copy over the new metadata in the file rather than the whole
file every time I update a tag?

Thanks