Back up iPhone to an external hard drive

You can create a Symbolic Link:

ln -s <path to the file/folder to be linked> <the path of the link to be created>

Do this on your own risk!

• Remove default Backup folder:

rm -rf ~/Library/Application\ Support/MobileSync/Backup

• Let's assume that, you mounted an External Hard Drive to /Volumes/Files then

mkdir /Volumes/Files/Backup
ln -s  /Volumes/Files/Backup/ ~/Library/Application\ Support/MobileSync

• Start iPhone backup as usual.
• You can unlink after you have completed your backup

unlink ~/Library/Application\ Support/MobileSync/Backup

That's it!

I understand what you want to do. The only way you are going to accomplish it is to install macOS on that external hard disk drive, boot from it, and then use it as you would normally use any Mac, including using it to back up your iPhone. The only difference is that your Mac will be slow to start from that hard disk drive, and it may be slow during operation as well.

But it will accomplish what you seek.

Back up your iPhone to a Mac, and back up the Mac to an external hard disk drive.

Back up and restore your iPhone, iPad, or iPod touch to your Mac or to iCloud - Apple Support

Back up your files with Time Machine on Mac - Apple Support

Follow the first set of instructions, after which you can copy the backup to another device and delete it from your Mac.

The iPhone backup can be found at:

~/Library/Application Support/MobileSync/Backup

If you want to be able to move your backup location to an external drive, it can be done but is tricky. I take it that you just want to be able to do it where all future backups will be stored on the external drive rather than on the boot drive. It can be disastrous if done incorrectly, but it can be done where Finder or iTunes uses a backup directory on an external drive.

I can’t provide the specific instructions here, but several sources have such instructions. It will require Terminal commands in Unix.

eamonn81 wrote:

I want to back up my iPhone to an external hard drive not to my Mac hard drive and then copy it over.

That is not an option. However, you can, instead, back your phone up to iCloud.

How to back up your iPhone or iPad with iCloud - Apple Support

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