Moving a big Photos library
QMy Photos library has grown to 400GB, so I must move it to an external drive. Can I just copy it across and delete the original?
AThe Photos library file you see in Finder is actually a package containing a well-defined set of folders containing info about your pics. Although the ‘file’ is easy to copy in Finder, it’s easy to inadvertently break things, so it’s worth doing this carefully.
Before doing anything, ensure that your current library is properly backed up – using Time Machine, for example – to a different disk than where it’s stored right now and where you’re moving it to. Next, use Disk Utility (in /Applications/ Utilities) to check the volume on the external drive where you want to the library to be stored is correctly formatted as either Mac OS Extended (Journaled) or APFS. Also, in Finder, select the drive, pick File > Get Info and check ‘Ignore ownership on this volume’ is ticked in the Sharing & Permissions section, where applicable.
Quit Photos and drag the Photos library to the external drive in Finder. When the copying process is complete, double-click that copy to open it in Photos, and check that it works there correctly. Go to Photos > Preferences > General and click the ‘Use as System Photo Library’ button.
Allow plenty of time for this setting to take effect, particularly if you’ve connected your library to iCloud. Once that’s working fine, you can drag the old Photos library to the Trash.