BackgroundWhen I installed an SSD in my Macbook Pro, I had to migrate all my files to new locations because the SSD is only 128 GB and my previous HDD was about 500 GB... and it was a little more than half full. So, where do I put them? I used another 500 GB external HDD (Firewire 800) as my Time Machine backup, so now I have 3 drives total. It took about a day, but I finally got everything shuffled around. This included moving my music to the external firewire drive, and thus, also my iTunes library.
At first, iTunes insisted on keeping the music library stored on my internal drive, in my home folder, in the Music directory. I told it "no, stop that!" several times but it persisted for some reason, refusing to accept my settings of putting the music library on an external drive. Finally, I nuked the silly empty library iTunes made when it started and couldn't find any existing one in my home folder, and closed iTunes.
iTunes has a couple files in the library folder: iTunes Library.xml and iTunes Music Library.xml. I don't know why there's two, but each one contained about the same things and were 30,000+ lines in length. There's also an important iTunes Library.itl file which is a binary representation of the library, which iTunes uses as its master copy of all your song titles, playlists, metadata, etc. Remove that, and iTunes will create a new empty one in its place. Remove the xml files, and iTunes will simply re-create them upon starting or closing (from the binary file).
I first tried opening iTunes with Option+Click which allows you to choose a new library (folder containing an ITL file) when it starts. This worked fine actually, except that none of the song files could be found: the library had moved to my external drive, but iTunes still expected them in my home folder.
So, I could locate them, one-by-one, or try something else.
The solution... for realz this time
After scouring Google for some time, I was finally led to this article in the Apple knowledge base, which describes how to restore an iTunes library. Summary:
First, since that KB article doesn't cover what to do when your library has moved, I had to figure this out. I opened both of those XML files and did a search-replace for the old paths with the new file paths. It's important to have iTunes closed in this process and not open it up until we're ready.
Then I dragged the ITL file (iTunes Library.itl) to the trash. And I dragged the two XML files to the desktop. Then I started iTunes. It created a new, empty library as expected. I changed the preferences so the library existed on my external hard drive in the folder I wanted. Then I did something very counter-intuitive, according to the KB article. I clicked File -> Library -> Import Playlist. Yeah, sure... except this isn't a playlist. It's a whole library.
However counter-intuitive this may seem, it worked for me. I chose iTunes Library.xml on my desktop and it restored the whole library like a charm. Now, whenever my drive is plugged in, iTunes just works. And when it's not plugged in, iTunes warns me and I can quit without messing anything up.