iCloud & iCloud Photos · iCloud Photos and the Photos library
How do I move my Photos library to an external drive and keep iCloud Photos working?
Short answer: Quit Photos, drag the library to an APFS external drive in Finder, Option-open Photos and pick it, then choose Use as System Photo Library in Photos → Settings → General so iCloud Photos keeps working.
Use Photos' own method: copy the library in Finder, open it in Photos, then make it the System Photo Library.
- Quit Photos.
- In Finder, drag Photos Library (in your Pictures folder) to the external drive. Use a drive formatted as APFS, and not one you use for Time Machine.
- Hold Option while opening Photos and choose the library on the external drive.
- In Photos → Settings → General, click Use as System Photo Library so iCloud Photos uses it.
- Once you've checked everything is there, you can delete the old library from Pictures to free the space.
Keep the drive connected whenever you open Photos. Storage Studio doesn't do this for you because Photos needs to make the switch itself — see why.