As I've mentioned before, I've been doing some serious culling of my iTunes collection of late. 'came time last night that I thought it's been a good long while since I've backed up my collection to the external; a trusty Maxtor II 250GB. Called Cortera BTW. Yeh I know, it's a geek pun but fellow Halo fans might get it, especially when you learn my iPod goes by the name Cortana...

For this I use a very nice freeware app produced by LaCie (thanks LC!) called SilverKeeper. It's a really good backup/sync tool that (unfortunately for me) does just what it's told. You can probably guess where this is going...

So here I was, plug in the external disk, fire up SilverKeeper, select source, destination folders, sync, then go.

Notice anything wrong with the above? I didn't.

Until about 20mins later when my MacBook Pro threw up an alert that it was critically short of disk space. WTF!? Check available space on the boot disk and sure enough it's at 0kB available. Several expletives later and I realise what I'd asked SilverKeeper to do. Do a two-way sync with my neatly pruned live iTunes collection folder and its bloated, weedy counterpart on the external. So now I had an iTunes folder with ooh a couple of thousand tracks in there that it a) didn't need, and b) didn't know about.

Aw crap.

First things first, the Mac is out of space. Step 1, stop that sync from trying to further roger it, step 2, free up some space pronto: Bad Things happen when a Mac (or any computer for that matter) has so little free space that it can't wiggle its toes.

After doing some quick deleting of some easy candidates (large downloads) I could afford the time to take a closer look. Here's where a brilliant app by the Omni Group comes in called OmniDiskSweeper. This critter does a simple job very well: it tells you exactly where your disk space has gone. Highly recommend it. Oh and by the way, do take the time to check out Omni Group's other products. They're seriously cool people, and do some mighty products.

OmniDiskSweep quickly identified a few candidates that took up a lot of space, and thanks to that I saw I still had a full install of Myst IV Revelations on disk (some 7GB) from my trip to the Gold Coast so deleting that gave me all the breathing space I needed to have a look at the debris.

So now I was faced with an iTunes folder on my internal disk that had many, many more large files in it that iTunes didn't know about. Craaaap...

I decided at that point to just leave well enough alone and leave it 'til morning (cue Chief Wiggum with loudhailer: "Back slowly away from the keyboard and no-one has to get hurt.") Geek that I am, the solution came to me in the wee hours of the morning.

The answer is iTunes itself.

Here's what I did:

1. Hook the MBP up to a drive with lots of space. Enough to take my entire collection. In this case it happened to be my work machine: an old Power Mac G4 which happened to have a large disk, booted into target disk mode. For those of you who don't know what that means, if you boot a reasonably current Mac with the T key held down it suddenly pretends it's nothing more than an external hard disk. Cool eh?

2. Hop into iTunes, then tell it (Prefs->Advanced) that its iTunes collection resides in a folder on said external hard disk. It'll take a little while to update its library database at this point.

3. Move everything iTunes knows about (but critically nothing else!) by choosing Advanced->Consolidate Library. Takes a long while but after this you'll end up with a perfectly accurate file representation of your iTunes collection.

4. Grit your teeth and delete your original iTunes collection!

5. Create a new iTunes collection folder to replace the old one, then do the opposite move, ie. change the collection location (as in step 2) back to the original location and (as in step 3) consolidate the library. Again, takes a long while.

After this, walk away, hands in pockets, whistling innocently.