If Santa has just brought you a nice new shiny SSD or you are running out of space on your HDD / SSD and are disgusted by how much space is actually used on backups of your iDevices you need this guide, it could save you gigs of space and is pretty easy to sort out!
The simple fact is we all need backups, but why not put them someone you want it to be instead of cluttering up vital space.
Before proceeding you might want to determine if this is necessary for you. Do this by checking the size of the iTunes “Backup” folder that we reference below, just click on it and select “Get Info” to calculate it’s size.
How to move the iPhone/iPod/iPad iTunes Backup Folder to an External Drive:
Note: Moving the iTunes iPhone/iPad/iPod backup folder to another drive requires that external drive to be connected in order to backup or sync future iOS devices properly.
From the Mac OS X Finder, hit Command+Shift+G to bring up the “Go To” window, type the following directory in:
From this folder, copy the “Backup” folder to a new location on the external hard drive, for the sake of this guide we’ll choose a folder called iOSBackup on a drive named “iTunes”
Before trashing the original folder, rename the existing Backup folder to something else for backup reasons, for example ‘Backup2’
Now we need to create a symbolic link between where the original Backup folder was, and the new location on the external drive. Launch Terminal and type the following command, referencing your new backup location:
ln -s /Volumes/iTunes/iOSBackup/ ~/Library/Application\ Support/MobileSync/Backup
(That command needs to be on a single line, formatting may look otherwise.)
Verify Symbolic Links:
To double-check that the symbolic link has been created, open ~/Library/Application Support/MobileSync/ in the Finder and look for the Backup folder, it should now have an arrow on the corner representing the symbolic link (think Aliases in terms of Mac OS X Finder)
Prevent Automatic Syncing of iOS Hardware:
Next you’ll want to disable automatic syncing of your iOS devices, because there are probably times when you’ll be plugging iOS hardware into your Mac without the external drive connected. Doing this is easy, just open iTunes > iTunes Preferences > click on “Devices” and then select the checkbox next to “Prevent iPods, iPhones, iPads from syncing automatically”
Test a Backup & Remove Backup2:
Finally, before removing the “Backup2″ folder and saving the disk space, you’ll want to complete a backup and sync of your iOS device to verify that everything is working as intended. There shouldn’t be any problems, but if there are, retrace the steps to make sure everything was done correctly. If the backup is fine, go ahead and remove the Backup2 folder and you can rely on the link to the external drive when it is connected.
Can I undo this? How do I move the iTunes Backup back to its default location?
Yes of course! If you ever want to undo this, simply remove the “Backup” symbolic link (the one with the little arrow icon) from ~/Library/Application Support/MobileSync/ by deleting it, and then moving your iOSBackup directory from the External Drive back to its original location. It’s that simple.
Will this work for all iOS devices?
Yes it should work fine with any iOS device including the iPhone, iPad, and iPod touch. If you use multiple iOS devices, they’re all stored in the Backup folder, which could make this tip even more useful since more backups = more space taken up locally.
The original article along with loads more great tips and such can be found here!