Then, next time you close Lightroom, the Back Up Catalog window appears. Check the filepath shown under Backup Folder to see where your Catalog backups are saved. Click the Choose button to change it if necessary, and the Back up button to complete the process. The important thing is to back your Catalog up to an external hard drive, so you don’t lose the backup if your main computer is lost or stolen.
Here are some important things to note about Catalog backups:
You only need to keep two or three backups. You can delete older ones.
Lightroom 6 and Lightroom Classic CC compress Catalog backups, saving hard drive space.
Once a month or so copy the latest backup to Dropbox, Google Drive or another cloud storage solution, in case you lose both your computer and your external hard drive to theft or fire.
The Catalog doesn’t contain your photos, only information about your photos. Photos need to be backed up separately.