Catalina wont boot from external SSD

socal59 wrote:

My late 2012 iMac is now running from an external Samsung SSD. It runs fine, but I wanted a more robust drive so I got a OWC SSD 1TB drive and a Mercury Elite Pro Mini enclosure.

I have the OWC connected with USB 3. I have downloaded a fresh copy of Catalina from the App store onto the drive, but when it comes to rebooting (picture of keyboard and mouse on screen) it looks like it goes to an old installer or something, because it just hangs and doesn't move. The original HD on the Mac is just used for Time Machine backups now. Could it still have an old installer confusing things?

It worked fine with my Samsung, but not with my OWC, which is, btw, erased and formatted as APFS, same as the Samsung.

What would make this work? Cloaning? Bootable drive?

Thanks in advance.

You can clone from one external USB drive to another external USB drive (Daisy chaining.)

No need for a fresh install, if you are currently not having issues.

Make a bootable clone of your main macOS drive that you are booted to (ie up and running)

to your new OWC SSD 1TB drive—and pickup right where you left off.

Use Carbon Copy Cloner—there is a trial version

ref: Boot clone https://discussions.apple.com/docs/DOC-10081

If you want a bootable USBinstaller of macOS Catalina, this can be done on a flash drive larger than 12GB

How to create a bootable installer for macOS - Apple Support

Contact OWC with your questions. Their customer support team should be able to provide you with the specific answers you're looking for.