Moving Photos Library To External Drive

I am still researching the new iMacs to see which one I am going to buy. For sure I will be getting an iMac with a 512 GB SSD, no Fusion Drive for me. I will have to make some room to go from my current 1 TB drive to the 512 SSD. The largest item on my current iMac (and probably yours as well) is the Photos Library. Mine is about 210 GB, my wife and I have lots of Photos. So, in preparation for the new smaller HD space, I moved my Photos Library to an external drive. Here is how that went.

Photos Library Move

There are all kinds of articles online about moving the Photos Library to external media. In my case I moved the library to an external USB 3.0 drive which contains a fast SanDisk SSD. You definitely do not want to move the library to external media that is a spinning hard drive. That will prove to be way too slow for sure.

After doing some research I chose to follow this procedure:

  • Copy the Photos Library from your Pictures Folder to an external disk.
  • Hold down the option (or alt) key and launch Photos. From the resulting menu select “Other library” and navigate to the new location.
  • You’ll get a message that says: “This library contains items that need to download from iCloud Photo Library.”
  • Click on delete incomplete items.
  • In the Photos app, go to Preferences and under General, click Use as System Photo Library.
  • Then go to System Preferences > iCloud > Photos > Options, Select iCloud Photo Library to turn that back on.
  • Test the library. When you’re sure all is well, feel free to trash the one on your internal HD or SSD to free up space.

This all looks pretty simple, but it took a while to get things working properly. Moving the 210 GB library was a slow process, but it moved to the external drive just fine. Here is how my Photos Library is setup now:

Library Setup

I have always chosen to keep my original photos on my Mac. I could always use the “Optimize Mac Storage” if I run out of room, but for now keeping the originals works best for me.

As you can see, the external Photos Library is selected on the external drive:

External Drive

It has been chosen as the “System Photo Library” as well. I have not deleted the version of the library on my main HD yet, but I will soon.

Here are some observations about this process. I backup my Photos Library to an external drive in a separate backup. Once I moved the library I had to setup that backup again in Chronosync and then back up the whole library. 

After moving everything I did some testing with the Photos App. All seemed to work well, although the Editing process is slightly slower than when the library was on my internal drive. A day or so after everything was moved I noticed that Photos uploaded all the photos to iCloud. That took a day or more of leaving the Photos App open. I suppose that is a necessary sync if you are displaying all your photos on all your devices through the iCloud setup. At any rate, if you do this I highly recommend just leaving the Photos App open overnight to see what it does with your setup. If nothing happens, then ‘no harm no foul’.


I am glad I got this library move completed. I will be all set to get my new iMac with the 512 GB SSD. That should be plenty of space for the remainder of my stuff. If Editing proves to be too slow in my new system, I can always get a Thunderbolt Drive for the library.