Back Up Your Disk
If you’ve read pretty much any book I’ve written about the Mac, you know I consider a solid backup plan to be essential for every Mac user. I hope you already perform backups regularly, and if you don’t, this is a perfect time to start.
Regardless of what you do normally (such as using Time Machine or Backblaze), I want to state emphatically that before upgrading to Catalina, you should create a specific type of backup called a bootable duplicate. That’s an exact copy of everything on your startup volume, stored on another disk in such a way that you could start up your Mac from that other disk and it would behave precisely as it does when you boot from your regular startup volume.
Even though the Catalina installer doesn’t ...