I have a MacBook Pro with two internal drives: an SSD and a slow rotational drive.

On the rotational drive I keep heavy, rarely accessed files like movies, photos, etc. These are symlinked from the SSD, so applications like iPhoto and iTunes will still find everything where they expect.

I don't usually have the rotational drive mounted because it's loud and mostly unused. Is there a way to mount it when the system tries to access data behind a symlink, then unmount it automatically later? (Intermediate *nix user, here, feel free to tell me I am asking for magic.)

Thanks for your help!