Question :

My internal HD is too full, so I want to make room for macOS to run smoothly again. As my Photos.app database is huge, would it be possible to move that database onto an external HD that is continuously connected to my Mac.

Is there any option to do so ?

Answer :

Yes, it is possible to move your entire Photos.app database to an external HD. Apple does explicitly recommend to use an external HD that is connected to your Mac directly with USB, ThunderBolt or FireWire. (and Apple explicitly recommends against putting your active Photos.app database on a wireless drive or network drive)

To do this, do this :

• get yourself an external HD, preferably one that is using a fast cable connection to connect to your Mac ; Samsung currently has some small and very good external HDs using USB-C for this : Samsung T5 Portable SSD
• plug the external HD into your Mac
• goto Applications –> Utilities –> Disk Utility
• open Disk Utility
• reformat the external HD as “Mac OS Extended”
• now, in the Finder, create a new folder on the external HD named Pictures
• then, in the Finder, goto Users –> [your name]  –> Pictures
• then drag&drop the Photos Library file to the external HD you have just created
• …this may take a while
• when done, open the Photos.app while pressing the [ALT]-key
• in the Choose Library window that opens, click on the “Other Library”-button
• from the pulldown Finder window, choose your new external drive –> Pictures –> Photos Library
• then click the Open-button
• now Photos.app will start up using the Photos Library on the external HD (and it will keep using the Photos Library on the external HD as its default library from now on)
• check inside Photos.app to see if all your photos are now available (there’s no reason why they wouldn’t but just to make sure…)
• now start using this setup as your new Photos.app setup, and if you don’t run into any problems in a few weeks (or even months if you need to) you can delete the Photos Library that was in the Pictures folder in your Home folder on your Mac’s internal drive to clear up some space

That’s it !

enjoy 😉