Backing up libraries

I create one library for every project I do. When I import media to an event, I leave files in place (I do not copy them to the library, in order to not duplicate clips).

All my media files as well as my library file are organized in a folder for that specific project.

I thought I could move that folder to an external backup disc when done with that project. But if I try and open the library and the project from the external drive, the project does no longer has the clips, as if they still point to the old location. As if the project does not point to clips through relative paths, but absolute paths. 

What am I supposed to do?

Try using the Relink function and point the missing files to the folder with the media.

Yes, that one did the job, thank you!