If you sync your iPhone, iPad or iPod touch on your Mac, you know that the first thing iTunes does is back it up (unless you've told it not to). Depending on the size of your device and how much data you have stored on it, this can gobble up dozens of gigabytes of space. Did you know you can move those backups to an external hard drive? You can, and we can walk you through how.
How to save space on your Mac by moving iPhone and iPad backups to an external drive
We've already gone over how to move your iTunes library to an external hard drive to save space, but did you know that iTunes may still be gobbling up space on your hard drive? That's because when you sync an iOS device on your Mac, it backs up the device to a hidden folder inside your home directory Library folder.
Hard drives on Macs are getting smaller as more and more systems use solid state storage, and our iOS devices are getting bigger. With some iPad and iPad mini models available in up to 128 GB of storage, that means iTunes can create some huge backup files.
Unfortunately, iTunes doesn't give us an easy way to move those backup files to an external drive. So we're going to use the Terminal app, found inside the Utilities folder, to do some UNIX command line magic to get it to work.
iTunes creates backup files for your iOS devices inside your home directory Library folder. The first step is to find that folder.
To access the Backup folder:
Open the Finder.
Hold down the Option key.
Click on the Go menu.
Find Application Support and open it.
Find MobileSync and open it.
That MobileSync folder contains a Backup folder, which includes iTunes' backup files for your iOS devices.
Attach your external hard drive. Drag that Backup folder to the external drive. You might want to put it in a clearly marked folder so you remember in the future what it's there for, like "ios_backup" or something similar.
Once you verify that it's been copied, rename but do note delete the original Backups folder (maybe call it old_Backups or something equally descriptive).
A note on aliases and symbolic links
Let me take a moment to explain this next step. We're going to use the Mac's Terminal app to create a symbolic link to trick iTunes into backing up onto your external drive rather than the boot drive.
Have you ever created an alias in the Finder? Aliases have been around since the classic Mac OS days. Aliases point to a file or folder that's kept elsewhere - it can be in another folder on your Mac's hard drive or another drive all together, even a server volume. They're handy ways of connecting to information you need to quickly and easily.
Unfortunately, some applications don't follow aliases properly. An older way of creating those sorts of connections is more reliable for actions like what we want iTunes to do: Symbolic links, or symlinks. They work at a low enough level that applications and operating system functions don't have as hard a time with them as they do aliases.
For the sake of the following example, I've unimaginatively named the external drive External. If yours is named differently, you'll need to change the /Volumes/External pathname in step 4.
To create a symbolic Backups folder link
Open the Finder.
Open the Utilities folder.
Double-click on Terminal.
type: ln -s /Volumes/External/ios_backup/Backup ~/Library/Application\ Support/MobileSync/Backup then press the Return key.
If you kept that MobileSync folder open, you'll see a new file created in it that looks like this:
The Finder says it's an alias. Don't be fooled. It's actually a symbolic link.
Now run iTunes and let it back up your iOS device. Make sure it's working by checking the creation date of the file you now see in the external drive backup folder. Assuming it's working, it's now safe for you to delete the old_Backups folder and get that precious hard drive space back.
One other thing: If it's unlikely that the external hard drive will be connected all the time, I'd recommend keeping iTunes from backing iOS devices automatically. To do so:
Click on the iTunes menu and select Preferences.... (Alternately, hold down the Command key and type ,.)
Click the Devices tab.
Check Prevent iPods, iPhones and iPads from syncing automatically.
Otherwise, when you try to back up your iPhone to a hard drive that's not connected, you're likely to see an error message that looks like this:
Hopefully you haven't run into any snags, but if you have any questions, let me know.