If you backup your iPhone, iPad or other iOS device to your Mac instead of to iCloud, then you’ve probably seen a noticeable increase in size used on your start up disk. This is because iOS backups can be multi-gigabyte files that take up considerable space; however, you may not… http://techdistrict.net/mobile/ios/how-to-backup-iphone-or-ipad-to-an-external-drive/