As an update, I've found notes I wrote about two years ago on this subject. I trust this is still correct, but if someone wants to look it over, that would be great:
How to move music to new EHD:
Background:
The Music application (formerly named iTunes) works by referencing a file and a folder:
1) a file named Music Library (formerly called iTunes Library.itl,) and
2) a folder named iTunes Media.
The Music Library file is a database of the songs in your library. It must reside in a specific location: Macintosh HD/Users/(your name)/Music/Music (to find it, in Finder choose Go > Home > Music > iTunes). Do not move this file from this location (I’m not sure you even can from within the Music application).
Your music is (or should be) in a folder named iTunes Media (it doesn’t have to be named this, as long as you're consistent with pointing the Music app to where the music files are located). This folder can be anywhere on your computer, whether on your iMac's hard drive or on an EHD, as long as the Music Library file knows where it is. To direct the Music application to where music files are stored, go to Music>Preferences, and on the Files tab, in the “Music Media folder location” box, make sure the location listed there is where your music files are (or change it to show the correct location).
Steps to move music to new EHD:
- Make sure you first backup your old EHD and your computer hard drive.
- On the new EHD, create a folder named “iTunes” and, within it, create a folder named “iTunes Media.”
- From the old EHD to the new EHD, copy all subfolders in the iTunes folder except the iTunes Media folder.
- Go to Music>Preferences, and on the Files tab, click the Change button for your iTunes Media folder location, then navigate to and select the iTunes Media folder on the new EHD. Also, make sure both “Keep Music Media folder organized” and “Copy files to Music Media folder when adding to library” are checked. Click OK.
- A message may say it's updating your iTunes library. It then asks if you would like to move and rename the files in your new iTunes Media folder to match the "Keep iTunes Media folder organized" preference. Click Yes.
- Once that’s done, you’ve moved the database file. It’s now time to move your music files to the new EHD. Go to File>Library>Organize library… Check “Consolidate files”. Click OK.
- The computer will now begin moving the music files. It will take about 4 hours to complete. Afterwards, check to make sure everything transferred well.