ITunes library trouble - after adding new external HD

Question

Hi. I was running out of room on an external drive, where I keep all my of my mp3s (my "media folder"). I purchased a new, larger external HD, plugged it in alongside the existing drive, and dragged and dropped everything in the empty new drive. So far, so good.
Now here's where I think I got a little too cute. Since the old ext HD was assigned the letter J:, I figured I could reassign the new drive as J:, and all would be jake --- all existing paths would point in the same direction, and iTunes wouldn't even notice the diff! (Or so I thought.) It actually went like this: reassign existing J: to letter O:; reassign new external (which was born L:) to J:.
When I reopened iTunes after the reassignment surgery, it was a tragic mess: all playlists gone, and the library had resorted to some way earlier version, with the dreaded exclamation points indicating that iTunes couldn't "locate" the music/media files.
I then proceeded to freak out, rapidly and rabidly re-selecting different iTunes library (.itl) files --- previous versions, latest versions --- but nothing was working. I fear all of this activity basically rendered the most recent library file all-but-irretrievable.
I've searched for all library files; I've restarted and rebooted. I'm not concerned about the mp3s themselves; I know where they all are, and can simply drop them all back into iTunes, no prob. What I'm still hoping to do is find that elusive, most recent library file and bring all of my precious, precious organization back.
Any ideas? I fear this is a classic example of (very) limited knowledge being a dangerous thing.
I'm running Windows 7; iTunes 11.1.0.126. MP3 files on an external, but iTunes folder on the C:/User drive, as by default (I think; not 100% sure).
Many thanks!!

Answer 1

Microsoft's SyncToy utility is ideal for this.  You can set up a "folder pair" consisting of the root iTunes folder on your master disc and the corresponding folder in your backup disc (you have options to sync all changes on both sides or to just echo changes to the master, including deletes, on the backup). Once you've done the initial copy you can run this folder pair in SyncToy to achieve what you want.
Are you using your existing external drive just for media storage or have you set it up as a fully portable library (i.e., your iTunes Library.itl file, Album Artwork folders, etc. are on the same drive as the media)?  If not, take a look at tt2's tutorial on make a split library portable - this will allow you to have everything used by iTunes on the external drive (better for portability as well as being more robust against PC problems).