How to backup efficiently and effectively iMovie 10.0
I was able to achieve the result I wanted using a tool that is available by default in Mac Os X and using the hardware I already have.

I've created a bash script with the following commands:

rsync -avz /Volumes/Snow\ Leopard\ Apps\ \&amp;\ Data/iMovie\ Projects.localized/ /Volumes/Backup\ 1/iMovie\ Projects.localized/
rsync -avz /Volumes/Snow\ Leopard\ Apps\ \&amp;\ Data/iMovie\ Events.localized/ /Volumes/Backup\ 1/iMovie\ Events.localized/
rsync -avz /Volumes/Snow\ Leopard\ Apps\ \&amp;\ Data/iMovie\ Library\ 1.imovielibrary/ /Volumes/Backup\ 1/iMovie\ Library\ 1.imovielibrary/


The rsync command will only copy the different part of the files or the new files changed since the last backup.

For this reason performance is blazing fast.

Then I also made sure that the script is executed automatically at every boot using this tutorial:
https://stackoverflow.com/questions/6442364/running-script-upon-login-mac