should I disconnect my external hard drive before installing Catalina

Hi egret2,

Yes, I would recommend disconnecting external hard drives before upgrading to MacOS Catalina to be on the safe side.

Also, don't forget to make a Time Machine backup before performing the update in case anything should happen.

I hope this helps.

I have successfully installed system upgrades with connected hard drives, but they were not powered on.

I am not advocating that you do the same, but to be safe, it wouldn't hurt to disconnect them.

egret2 wrote:

should I disconnect my external hard drive before installing Catalina

Sure why not?