Let me start my saying that I am trying to use an unsupported, non-recommended set-up. I want to store my iTunes library on my Linux server in an NFS-mounted directory. Why? I bought a 60 GB PowerBook instead of an 80GB, and figured I didn't need to have the music taking up disk space (especially when I have a 200GB disk sitting here on the network). iTunes has an option to specify a different iTunes Music folder location (Preferences, Advanced, General).
The only problem I had (I thought) was when I fired up iTunes (or my PowerBook did in response to plugging my iPod in—I've switched that off also) and my server was turned off. iTunes insisted on resetting my iTunes directory back to the default instead of giving me an error message. It showed that a whole bunch of music was missing (of course) and stored new purchases or newly ripped music into the default location again. But, I thought that the only problem I had was that occasionally music or podcasts would end up in the wrong place, and I would move them.
Then yesterday, it happened and in the course of trying to fix things, I found that some music was missing. The missing music was on my iPod, but I could not find it anywhere on my PowerBook or my Linux server. Yipes! I was, of course, happy that it was on my iPod. But, iTunes has no mechanism to update your music library from the iPod, only vice versa. You can mount the iPod, of course, as a disk, but that gives you no access to the iPod music section.
I am not clear as to what happened or why, but I do think it has to do with the iTunes client preferring local storage and insisting on changing back to it when the configured directory is unavailable. (I'd like it to complain and give me a choice.)
In another entry, I'll discuss the program I found and used; it saved me from hours of frustration.