How to cope with a Photos library too big to fit on an internal Mac drive

iCloud Photos lets you have your picture of a cake and shoot a video of eating it, too. You can create a library of images and movies that’s far larger than the storage space available on any linked iOS or macOS device without losing anything you’ve captured.

Apple accomplishes this by treating iCloud as the “truth.” It stores the original, high-resolution versions of your media in your iCloud storage, while providing the option to store only “optimized” or thumbnail versions that take up a fraction of the space on your Mac, iPhone, or iPad.

You can choose to download the full-scale originals, but you obviously need to have enough storage to hold the library.

If you don’t have an iOS device with the capacity or a Mac with a big enough internal or always-connected external drive, you have to rely entirely on Apple retaining the high-resolution originals. About 18 months ago, I wrote a column aptly titled, “Why you should not rely on iCloud Photo Library as your only media backup.” I meant it then and now.

The gist is that it’s risky to trust someone else, anyone else—even Apple—with the only backup of your stuff. Apple tends to encourage that these days with iCloud. And the company has been trustworthy with your data. But I still think we should always want and expect to have at least one—but typically multiple—complete copies of our important data in our possession or fully under our control.

Is there a way to work around this? Not easily. Apple didn’t plan for this scenario. There’s no option at to “download all media from iCloud,” and iCloud as a service doesn’t offer an interface for third-party backup services, like Backblaze or Carbonite, to extract or regularly update such a backup, either.

While Photos for macOS lets you maintain multiple Photos libraries, only one library at a time can be designated the System Photo Library, and only the System Photo Library can sync with iCloud Photos.

The obvious solution would be to use an external drive to hold your Photos library. Apple makes it quite easy to move your library and point Photos to it, including syncing to iCloud Photos from that migrated library. (See “How to move an Apple Photos for OS X library to an external drive.” The column is from 2015, but the instructions remain accurate.)