If you don’t spend a lot of money and roll with a multi-terabyte internal drive you probably have to store your Photos.app library on an external one. I’m always curious how people actually do that because for a variety of reasons like analyzing faces, transcoding and other tasks Photos.app is constantly working in the background and making it impossible to eject my external disks. I usually “Force Eject” them via the Finder which then results in a corrupted library from time to time.
Fixing it sometimes works. If it doesn’t, Apple tells you very clearly what’s wrong: 1000.