Your iTunes library is very important, housing music, TV shows and more. However, it can also swell to huge proportions. There may come a time when your iTunes library outgrows your Mac, especially if you transfer from a desktop with a huge hard drive to a MacBook Air with a relatively tiny SSD.

Should this happen, you’ve three choices: madly prune your collection; move the iTunes library to a different Mac that has more disk space; or copy the iTunes library to an external drive. We figure you can take care of the first option yourself, and so we’ll concentrate on the other two.

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How to move your iTunes library to another Mac

When migrating to a brand-new Mac that has comparable storage to the old one, OS X’s Migration Assistant is your best bet, automatically transferring content for you. However, it’s also possible to manually transfer your library to another machine, eventually leaving the one you copy it from with lots of free drive space.

On the Mac you want to copy from (the source Mac), go to System Preferences and open Sharing. In the services list, turn on File Sharing. On the Mac you’re copying to (the destination Mac), your source Mac should appear in the Shared section of the Finder sidebar. Select it and click Connect As. (If it doesn’t appear, use Go > Connect to Server from the Finder menu, and type in the server address that’s shown in the aforementioned Sharing pane.) In the sign-in dialog, select Registered User and type the name and password for the source Mac. Read next: How to create playlists on your iPhone or iPad.

Navigate to ~/Music on the dialog showing the source Mac’s file system and drag the entire iTunes folder to the equivalent location on the destination Mac. Depending on the size of the library, the transfer could take a long time. (Note if you’ve a back-up clone of the source Mac, connecting that to the destination Mac and copying from it instead might be quicker. Also, this kind of copy is destructive, and so it will overwrite all iTunes content on the destination Mac. If there’s already unique content in iTunes on that Mac, copy it elsewhere, if necessary.) Read next: How to submit a Podcast to iTunes.

Once the copy is complete, authorise the destination Mac to play content bought from the iTunes Store that has digital rights management. Once you’ve tested whether the copy worked fine, you can delete the iTunes library from the source Mac. For safety, first making a temporary second copy of it to a separate drive, just in case, is a good idea though. Remember to deauthorize any old Macs you’re planning to no longer use.

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How to move iTunes library to an external drive

Another option if your iTunes library’s too big is to copy everything to an external drive. To perform this you'll first want to enable 'External disks' and 'Hard disks' in your Mac's Preferences, found under the Finder menu.

Once you've enabled the option, you can proceed in dragging the iTunes backup from your old computer to your external hard drive. To locate the Music folder on your Mac, locate the Home option in the Finder menu, then double click the Music folder. 

Within the Music folder, you'll find the iTunes folder, which you'll want to drag and drop into your Hard Drive. This will now move your iTunes files to your external hard drive. Depending on the size of your music collection, it might take longer.

After you’ve done, you'll want to relaunch iTunes, by holding down the Option (Alt) key and clicking on the iTunes application. This will then prompt you to choose a new library. Read next: What is the Option Key on a Mac.

In the Choose iTunes Library dialog, click Choose Library and select the iTunes folder on your external drive. This can be enough for iTunes to properly associate itself with the copied library, but it’s also worth going into the Advanced preferences and checking that the iTunes Media folder location is correct. If not, click Change and reconfirm.

When using external drives, some things are worth bearing in mind. First, unless the drive is mounted, you won’t have access to your iTunes files. On that basis, a tiny USB Flash drive is a good bet (if you can get one that’s big enough) rather than a large external hard drive. Also, while you can use a networked drive’s iTunes library, do so with caution, and don’t try to connect multiple iterations of iTunes to it.

Finally, if your media content is important to you, ensure you have multiple copies of it. This means if you’re backing up your Mac you should also be backing up the external drive with your iTunes library stored on it. If you don’t, there may come a day when you want to play your favourite songs and all you find is silence from a dead drive.