back-up and mirroring software recommendation

Hello,
I am looking for recommendation;

I want to be able to do all editing, labeling, rating in LR or Adobe bridge on files residing on my internal HD and then have those changes reflected in the files on the external HD which was used as back-up drive at the time of initial file ingestion.

This update of files on the external back-up HD would be done at some later date, when editing is completed on the internal HD.
What software would be good for that?
Thanks!