I just have 80 Gig on my harddrive and this is quite less when doing development work at daytime and music in nighttime – in fact, it’s not possible to have more bigger music project at the same time with this space. The loops (i don’t use them, but installed them to see what’s behind that stuff) take more gigs than i can efford, same goes for the garageband instruments.
This morning i had a reinstall and decided to put all that space consuming stuff on my external harddisk. If you want to do like i did, i recommend you about 300 Gig space on a Mac OSX journaled filesystem. I had a FAT32 on my mac to get on it via Windows too, but this harddisk is not always activated when i need it. I have to make a harddisk check to activate it, which is quite uncomfortable. I guess you don’t want to have that problems with your instruments.
However, having your instruments on an external disk is straightforward. Please note, my volumes name is FELIX, replace that name with whatever you call your harddrives.
LOOPS
I created the folder:
/Volumes/FELIX/audiolib/loops/Apple Loops/Apple
With my Finder I clicked at “Macintosh HD”, where my loops are currently installed. Switch further to
/Library/Audio/Apple Loops/Apple
and copy all that folder in there to your new Loops-Folder (and delete the old content). You can do the same with “iLife Sound Effects” if you want. Cause you instrument installer indexed all that loops, you have to go to:
/Library/Audio/Apple Loops/
and delete all txt files in there (maybe three or four or simliar- depends on how much Jam Packs you installed, i guess). Start up GarageBand and open you Loop-Browser. It will tell you that you don’t have any Loops installed. Open your finder with your new loops-place, drag the folder where all subfolders with instruments are and drop the into your loop-browser. GarageBand does the rest for you.
INSTRUMENTS
It’s a similar process for your instruments. I created:
/Volumes/FELIX/audiolib/instruments
Then i copied everything from /Library/Application Support/GarageBand/Instrument Library to this folder. I emptied the Instrument Library Folder. Please note: if you have some stuff allready installed in you new folder (FELIX in my enviroment) pleas copy carefully. OSX will delete old stuff when you just copy folders, and this is not what we want. In this case you have to copy manually file for file. And: you’ll need your superuser password for this action. If you don’t have any yet, open a terminal:
> sudo su
This will ask you for a password. By default you have none. Press enter. If you are in without error message, do this command:
> passwd
and get a new password. By the way, you should do this ALWAYS, it’s a bad idea not to set a superuser password – everybody can login and manipulate your computer this way.
Before you do that, of course i cannot give any guarantees. And please note, i have some kind of bug with my method, if you know how to fix that, let me know. All my instruments are now in the same JamPack, which may be a result of my heavy metal copy actions 
When you next start up GarageBand i tells you that it has no Instruments installed. There is “Choose” Button where you can point to your new Instruments folder.
