I have a 2TB external drive that I've been using for all my iMovie 9 events and projects. After upgrading to iMovie 10, I noticed that my new iMove Library file was 1.1 TB and the pre-existing iMovie Events folder was also 1.1 TB. Add to that the fact that I have several other folders adding up to about 800GB, and you would "think" that I have 3TB of data on this 2TB drive.
So, I did a little digging suspecting that Apple is using the same method they use with Time Machine and sure enough, they are doing so.
Basically, they are creating a second hard link to the movie file within the iMovie project. You can read about hard links here: http://linuxcommando.blogspot.com/2008/09/how-to-find-and-delete-all-hard-links. html
That is also why Apple is saying that you can safely delete the pre-existing folders after you've successfully updated: http://support.apple.com/kb/HT5917
Here is an example of one of my folders deep into the new iMovie Library:
mbp17-air:Original Media jeff$ ls -lh
total 42420856
-rw-r--r--@ 2 jeff staff 1.1G Dec 24 1998 clip-135-02-05 05;27;15 1-1.mov
-rw-r--r--@ 2 jeff staff 169M Dec 25 1998 clip-135-02-05 05;27;15 1-2.mov
-rw-r--r--@ 2 jeff staff 49M Dec 25 1998 clip-135-02-05 05;27;15 1-3-0.mov
-rw-r--r--@ 2 jeff staff 6.4G Dec 25 1998 clip-135-02-05 05;27;15 1-3-1.mov
-rw-r--r--@ 2 jeff staff 8.2G Dec 25 1998 clip-135-02-05 05;27;15 1-4.mov
-rw-r--r--@ 2 jeff staff 1.9G Dec 25 1998 clip-135-02-05 05;27;15 1-5.mov
-rw-r--r--@ 2 jeff staff 2.4G Dec 26 1998 clip-135-02-05 05;27;15 1-6.mov
See that #2 after the @ and before the jeff on each line? That indicates that this file is linked in 2 different places, hence the upgrade isn't duplicating the movie file space. All in all, pretty nice use of hard links I think!
kazooless
