When you first use Photos, you create a new library or select the library that you want to use. You’ll need to properly manage them, including taking steps to make sure you don’t run out of local storage.
You can create multiple photo libraries on your Mac, but you have to choose one to be THE System Photo Library. Photos in it are available in apps like iMovie, Pages, and Keynote. You can also sync them to iOS devices and Apple TV via iTunes. If you want to use your own images as your desktop picture or screen saver, the images need to be in your System Photo Library before you can select them in System Preferences. Plus, some Apple apps and third-party apps also access your System Photo Library using the Media Browser.
If you have only one photo library, as most folks do, it’s the System Photo Library. If you have more than one, the first photo library that you create or open in Photos will become the System Photo Library.
By default, your System Photo Library is stored in the Pictures folder on your Mac. If, like me, you take lots of pics, hard drive or solid state drive can fill up easily, especially since more Macs ship with limited storage. However, you can move the System Photo Library to an external storage device. Make sure you’ve backed up your photos, quit Photos, then:
- 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.
Note that, if a Photos library is located on an external drive, don’t use Time Machine to store a backup on that external drive. The permissions for your Photos library may conflict with those for the Time Machine backup.
If you want, you can create additional photo libraries and store them in any location on your Mac or on an external storage device.
If you do have multiple libraries, your can only work with the photos in only one library at a time. To work with photos in another library, you must switch between photo libraries. To do this:
- Hold down the option key on your keyboard.
- Double click on Photos.
- Click on the name of the library you want to open.
If you switch to a library other than the System Photo Library, the changes you make aren’t reflected in iCloud Photos, because iCloud Photos only syncs changes from your System Photo Library.
Note that, by default, all the files you import into Photos are stored in the current photo library. If you want, you can set Photos to leave the files you import in their original locations (for example, on a storage device) and not place them in the library.