You can simply copy the contents of the 2tb drive to the 3tb drive and you will be fine. The only issue you will have is when you open the backup copy of the project you will have to relink the footage. As long as you haven't changed the file structure of your footage backup, you only have to find one clip and it will automatically find all other assets.
There is also a way to condense the projects and copy for backup, using the project manager. The only thing Adobe seems to have forgotten is AE comps from Dynamic link, you'd have to manually back those up for each project if you do it this way.
Here's a little video tutorial on it http://layersmagazine.com/using-the-project-manager-in-premiere-pro.html
Paul this sounds good. One question though. My 2tb has the footage only. So, in addition to the footage being backed up, what other files do I need for backup? Is it only .PRPROJ file?
See the manual under archiving projects.
Basically, with PPro up and a project open, click on Project...Project Manager. Make your settings, pick a destination, and turn it loose.
Note that PPro doesn't include any AE, Audition, etc. projects when doing this. So you'll want to see to the AE and other applications also. Which is too bad -- it would be really nice if Adobe would make backing up the entire project, all the pieces accross all the Adobe applications, simple and easy. If you want that too, make a request using the Feature Request tool like I did.
Thanks Paul (and others responding too),
That layersmagazine.com article video was great. I think I'm all set.
The prproj file is the only file you NEED to back up along with all of your footage and assets (images, audio files, all media used to create the project). You can also copy the autosave files and render files if you would like, but they are not needed. I would suggest looking at the file structure John suggested, I use a very similar file structure and it's really helpful when it comes to organizing and backing up my work.
Cool. My workflow usually has me brining in my video/audio footage assets to my primary 2TB external drive, and then immediately I do a backup of the footage assets to separate backup 3TB drive. So given I already have those assets backed up to the 3TB, I guess I can just do a "Save A Copy" and save it to the separate 3TB? (And wouldn't that save the .PPROJ file WITH ANY AE comps/Photoshop Titles I had created and used in my .PRPROJ file? )