Backup iPhone to an external drive with iTunes on a Mac 4/26/16

I’ve been having serious problems with my iPhone 6 battery ¹, and before I take it to an Apple Store, I wanted to backup my phone using iTunes ². However, my Mac only has a 256GB hard drive, so space is at a premium. Rather than shuffle work files off, I tricked iTunes into backing up my phone data to an external disk using the power of symlinks.

These are the steps you can take if you want to do the same thing:

Be careful, I’m not responsible if you nuke your hard drive or existing backup data, backup your Mac to Time Machine and your phone to iCloud first
Open Terminal and type open ~/Library/Application\ Support/MobileSync/ and press [Return]
In the Finder window that opens, rename the Backup folder to something like Backup-local
Plug in an external hard drive (I used a 32GB SD Card, you might need something bigger depending on your iOS device)
Open the external disk in finder, and create a folder called Backup
Open Terminal and type ln -s
Drag your new Backup folder from Finder into Terminal after the ln -s you just typed
Finish the command by typing ~/Library/Application\ Support/MobileSync/ and press [Return]
If you go back to the MobileSync folder we opened in step 2, you should see a new Backup folder with a little alias arrow in the bottom left of the icon
Go into iTunes and start your encrypted backup

If everything worked right, you should see your external hard drive Backup folder fill with backup data. Reverting the process shouldn’t take more than removing the symlinked Backup folder and renaming Backup-local back to Backup.

My phone runs out of juice in the early afternoon. It also frequently jumps from ~50% to ~30% to 1% to dead within minutes. Plugging the phone into power will often immediately restore the battery to ~40% power after a minute or two of charging. ↩
iCloud backups are great, but restoring from them takes forever. ↩