Backup 3 has a useful option to back up just your iTMS purchased files. But, it’ll only work for files in your user’s iTunes directory. And I store my files on an external drive.

But, I found a way to back up my iTMS files from a different disk…

Make a copy of:

/Library/Application Support/Backup/com.apple.iTunes.PurchasedMusic.quickpick

and call it something like

com.apple.iTunes.PurchasedMusicExternal.quickpick

Right-click on the new file, and select “Show Package Contents”

Browse to the file at “Contents/Versions/1.0/Resources/DefinitionPlist.strings”, and open this in a text editor

Change the pattern text to be (e.g.):

pattern = “/Volumes/Elephant/iTunes Music”

I store my music on an external FireWire disk called Elephant, in a folder called “iTunes Music” at the root of the disk. Set your pattern string to match where your own music is stored.

Save and close this file. Then, open English.lproj/infoPlist.strings in a text editor (if you’re not English, open the appropriate language for you).

Amend the “Description” and “Name” to mention your external disk, e.g. for me:

“Description” = “Backs up only the music files purchased from the iTunes Music Store and iTunes playlists in the iTunes folder located on Elephant.”;

“QuickPick Info Archive Version” = “1″;

“Name” = “iTunes purchased music on Elephant”;

Save and close this text file.

Now, launch Backup, and you should find that you have a new QuickPick, which finds your iTMS files on the external disk :-)