Thanks for the reply. First, the answers to your questions:

Yes, I let iTunes keep the folders organized, which thus far has ensured that the two individual music folders are identical in every way except for file size and types (ACC vs lossless).

Yes, the music folders are completely separate. Currently they are on the same drive, but there have been times in the past when they were not - specifically, the lossless files have always been on the same hard drive. At various times it has been more convenient to keep the ACC folder on an internal drive. The location of this folder has never been an issue, as iTunes is either pointing at one or the other, never both at the same time.

I'm not sure I'm reading your third question correctly, but each file type folder has the same multi-folder organization within it. In other words, currently, on that hard disk, there are two folders, one labeled "Compressed Music" one labeled "Lossless Music" if I open either one of them, I see a list of all of the various bands and artists for which I have music. If I go to the folder for "The Beatles" and open it, I see a list of folders for specific albums. If I go to "Revolver" and open it, then I see the list of specific songs, and this is the only place that the two folders differ. One has the file "01 Taxman.m4a" at the top which is 3 mb in size, the other has "01 Taxman.m4a" at the top which is 16 mb in size. This is the first time I've noticed that the lossless and ACC files use the same file extension, which is strange, but nevertheless, this is how the two distinct folders are set up, and this has worked for two years runnning. This multi folder organization by artist and then album and finally song was the way itunes wanted to set things up, and I saw no reason to stop it or do otherwise.

Switching between the folders was (and should be) as easy as going into advance preferences, changing the "itunes music folder location" to the wanted folder (either Compressed Music or Lossless Music) and letting itunes update and organize itself. With this volume of music, switching between folders takes several minutes, but since I only do it once every month or two, when I need to update my ipod with the new CD's I've bought and burned, that time lag is not really an issue.

"I cannot think of why iTunes would find the contents of one folder but
not another. If you simply look at your music library in iTunes, as
opposed to the specific folder contents, do you still get the missing
link icons?"

• Let me emphasize that the music folders are not affected, only the iTunes library is, and only by not pointing to the right places. All songs are still present when I open itunes, just most of them have the exclamation marks on the left side indicating that the program is not seeing the file to which it should be pointing.

"If you tell iTunes to play music from a particular folder, then it
should do so. For instance, if I have my “R&B (1990s)” folder
selected and start playing music iTunes should not be playing music
from my “Rock (1980s)” folder."

- it sounds as though you feel the issue is with playlists. This is not the case at all. Your wording makes me wonder if you've told itunes to organize your music differently, or if you are talking about playlist folders. the playlists have nothing to do with this issue, and nothing to do with how the music is organized on the hard drives (question 3, above).

"I am not sure of what iTunes behavior would be if a song is missing a
link to a file, but I would guess that the track would be skipped. In
your case, because you have duplicates in another format, perhaps
iTunes is intelligent enough to seek duplicate songs; as a result
iTunes may be switching to your AAC folder."

You are right, that if itunes is missing a file link for a song that it will skip that song when playing, but that's just a side effect. iTunes does not look for the original file and then revert to the ACC folder or go there alternately - it just doesn't look for the file in the first place. The music is not missing... (as I mentioned before) once I individually point iTunes to the file it says it can't find, it's happy again. I'm just trying to find a way not to have to do that 6,000 times, or to have to rebuild the library completely (thereby losing all my playlists, song rankings and other information). And to find out what is causing the issue, so that this doesn't happen again.

Incidentally, I too thought this through quite carefully before burning any of my music. This dual file structure seemed the best answer, and worked perfectly in small scale tests in the days before I started the massive process of burning thousands of CD's to hard drive (and worked flawlessly for two years with the full library as well, of course) and in several weeks of searching before hand, I didn't find anyone with a better solution to the issue. I understand your recommendation against getting rid of the original CD's, but that was a big part of the point. I was beginning a job where I would be traveling (and moving) a great deal, and a couple thousand CD's are no small effort to keep, store, organize and move. Selling them off more than paid for the expense of buying a couple good hard drives to store the music, and with the exception of two CD's which I discovered later were slightly corrupted in the burning process, and which I didn't listen to before selling them off (which I did with all my favorite music), there have been no losses or downsides to to this migration at all. Just the opposite... I enjoy my music collection more than I ever did when I had to look through shelves and shelves of CD's to find the one I was looking for.

In addition, with one hard drive sitting on the desk holding my music as well as my other work, if I am home when there is a fire or other incident, unplugging the drive and carrying it out the door with me will save not only my work, but my entire music collection - something that would have been impossible with a couple thousand CDs. I'm currently investigating off site backup as well, and at the very least, am considering buying a cheap hard drive to copy my work and music files and keep at my parent's home, as an easy off-site long term insurance (especially since my neighbors in the next apartment started a fire a week ago!). While in the ideal world, I'd have all the CD's sitting around, the fact is, my music collection is at least as safe, if not safer, like this than it was when I owned the CDs, and I don't have to break my back everytime I move.

Hopefully that didn't sound defensive... I realize that not everyone wants to sell off a massive music collection and just keep it virtually, but my feeling is that just like LP's (aside from a few diehard collectors) most people will head that direction in a few years. For my lifestyle, carrying around a couple hard drives is far easier than a dozen or more milk crates weighing 30 lbs each.

Thanks again for your reply,

Stephen

Someone reminded me of this thread today, and I thought I'd come back and share what I learned. First off, as far as the original problem - that of ituns not being able to spot things, and me having to go through and point them out individually, song by song - I never really got past that. I spent about three hours in front of my computer getting carpal tunnel, pointing it to the proper location of all the songs. Once I got everything happy again, with no little exclamation points, I did some major organizing. I went through and took all the greatest hits and albums that got put into "complilations" when they really didn't belong there, and I moved them were they needed to be. I went through and consolidated the various spellings of band names into one folder (ie. Billy Bragg and Wilco on Mermaid Ave. 1, but Billy Bragg & Wilco on Mermaid Ave 2, which itunes put in two different folders, of course. 6 albums by Steven Ray Vaughn and Double Trouble had no less than 4 folders!). I cleaned everything up and made it as logical as I possibly could, then I threw out my old AAC music folders, and set my Mac Pro to convert all 7,800 songs from lossless to AAC, and place them in a new music folder. That went faster than I expected, but still took around 24 hours. When it was done, I had two folders in my itunes music file, exactly the same, but one lossless, at around 250 gb in size, and one compressed, at about 48 gb in size. From there, all I had to do was figure out how to make iTunes switch from one to another, without getting confused. (and sadly, this means that the next time I plugged in my ipod, iTunes would only let me sync to the new library by erasing and starting over, which meant that I lost all the ratings and playlist data on the ipod... sad since I'd "discovered" many songs I didn't know while traveling through Europe over six months and listening to the ipod a lot. Now I have to/get to rediscover them again. Eventually.)

Essentially, the issue is in that while iTunes 7 wil let you create multiple libraries, which is what I needed all along, it will not let those libraries have different preference settings. What I really needed, was a way to make two identical libraries (in terms of folder structure) but with different preference settings - one set to import apple lossless, and point towards a folder in my itunes music called "lossless", and one set to import in AAC compression, point to a folder in my itunes music called "aac". After a great deal of research, it seems that Apple does not provide a way to do this. The good news is that others do.

I found a few different programs: iTunes Library Manager, Libra, and Multitunes. None of them work quite as seemlessly as I think they should, but all will let you run different music libraries with different preference settings, which is what I needed. In the end, I have been using multitunes, which works inside of itunes, and simply adds an option in the advanced drop down menu to switch libraries. Selecting that option will close itunes, then reopen it with the new library and preferences. This still isn't a perfect solution... For one thing, everytime I buy a new CD, I basically have to import it twice, once as the lossless file, then switching libraries, and importing as a compressed file. There are other ways to do that (convering the lossless, dragging, etc) but none of them are convenient. The bigger annoyance is that there are two completely different sets of user data on the two libraries, in terms of song ratings, most played, last played, etc. One set which reflects what I've been listening to through the main system, the other reflecting what I listen to on my ipod (though I should point out that they started from the same place - where I converted the lossless library to the AAC.. they've just been diverging ever since, and will contineue to do so). In the ideal world, that data would be shared, and when I rate the new song by White Stripes a 5 on my main system, the ipod would know I liked it as well, but because of the way this stuff works, that simply isn't going to happen... at least not until Apple recognizes the need to let their multiple libraries carry different preference settings (and probably not even then, as it would probably be a pain sorting out which part of those preferences files they could share, and which ones they couldn't.)

So, that's how I'm running my system now. I wish it were prettier, but at least it's running smoothly and iTunes is able to find everything again. As far as I can tell, even if some things go wacky, I shouldn't have to go through and manually point songs ever again.

Hopefully this will help some others if they get into a similar fix, and maybe spur Apple to think a bit more about how people are managing their massive libraries of music.

Best,

Stephen