The Full Hard Drive
macOS tightly integrates with iCloud to ensure your data is backed up and accessible across all your Apple devices. If you take a picture on your iPhone, the iCloud Photo Library automatically syncs it to the Photos app on your Mac. This is a brilliant feature until your Mac starts running out of internal storage space. The Photos app, by default, attempts to download the full-resolution original file for every single photo and video in your iCloud library. If you have a 500GB iCloud plan but only a 256GB SSD in your MacBook, this automatic syncing will rapidly consume every megabyte of available space, bringing your computer to a halt.
Managing Photo Storage
To protect your local storage space and stop macOS from automatically downloading and syncing every full-resolution photo from iCloud to your Mac’s hard drive, you must change how the Photos app manages its library.
Open the Photos application on your Mac. In the menu bar at the top of the screen, click on Photos, then select Settings (or Preferences). A new dialogue box will appear. Click on the iCloud tab at the top. Ensure the checkbox for “iCloud Photos” remains checked so you can still view your library. However, look directly below that checkbox. By default, “Download Originals to this Mac” is likely selected. You must change this setting by clicking the radio button for Optimize Mac Storage. By doing this, macOS will keep full-resolution copies safely in iCloud, but will only store small, space-saving thumbnails on your Mac, downloading the large originals only when you specifically double-click to edit or export a particular photo.