Mac storage basics · Photos, music and video
Can I split my photos into more than one Photos library to save space?
Short answer: Yes — hold Option while opening Photos and choose Create New. Only one library is open at a time and only the System Photo Library syncs with iCloud.
Yes. Hold Option while opening Photos and click Create New to make another library — for example an archive library kept on an external drive. You can only have one library open at a time, and only the System Photo Library syncs with iCloud Photos.
A common approach is to keep recent photos in the main library and export or import older years into an archive library on an external drive. Always keep a backup of each library, because an archive on a single drive is only one copy.