Problem Installing Big Sur Beta 3 on an external SSD on a Supported Mac

[macsba]

I'm testing the Big Sur beta on an external SSD connected to a supporting iMac (2017). I've downloaded the full ~ 12GB installer. It does it's thing of installing the first payload. Upon restart, the iMac goes back to the internal SSD. Yeah, can't complete the installation. Tried it a few times to install beta 3 but still greeted with the internal SSD.

How can I get the beta 3 installer to go to the Big Sur installation volume? Feeling a bit lost here. Thank you.

 

[Barry K. Nathan]

I'm testing the Big Sur beta on an external SSD connected to a supporting iMac (2017). I've downloaded the full ~ 12GB installer. It does it's thing of installing the first payload. Upon restart, the iMac goes back to the internal SSD. Yeah, can't complete the installation. Tried it a few times to install beta 3 but still greeted with the internal SSD.

How can I get the beta 3 installer to go to the Big Sur installation volume? Feeling a bit lost here. Thank you.

I've seen situations where some USB 3 enclosures aren't consistently bootable on Macs. First try installing High Sierra, Mojave, or Catalina on the external SSD to make sure the problem really lies with Big Sur and not with the SSD or its enclosure.

 

[macsba]

I've seen situations where some USB 3 enclosures aren't consistently bootable on Macs. First try installing High Sierra, Mojave, or Catalina on the external SSD to make sure the problem really lies with Big Sur and not with the SSD or its enclosure.

Thanks Barry;

I did part of your solution. What I did was to move the external SSD from the USB 3 port to the Thunderbolt 3 port. Still it wouldn't install, I ended up nuking the external SSD and cloning the internal SSD to the external SSD. I was able to install Big Sur beta 3 on the external SSD. Booting off of it works well. However I did find a bug in beta 3, the clock display can't display the time in the 24 hour format - settings didn't work.

Anyway, thank you for your assistance.