Unable to Install macOS on External Drive

[macrlz9]

Hello!
I’m having a strange issue I’ve never had before. I have a 16” MacBook Pro and am trying to install macOS 10.15.3 on an external USB flash drive (connected via Apple’s USB-C to USB adapter.

• I boot into Recovery (Command R)
• Disable all T2 features (security and allow external drive booting)
• Erase the drive GUID APFS
• Select the USB drive to install macOS
• It goes through the install but reboots and gets stuck at the Apple logo and progress bar (without time remaining indicating that the actual install has completed and is trying to boot). The machine will eventually reboot and get stuck again then reboot, etc.

I’ve also tried using Super Duper to clone an existing Catalina install to the USB drive which is also not quite working. It was doing the same boot loop but if I use safe mode (Shift), after an extremely long time... like an hour, the login screen will come up but it’s so unresponsive I can’t even login. After entering my password, it just eventually gives up, screen goes blank and machine either shuts off or completely locks up.

I’ve installed macOS on an external drive so many times and have never had a problem.

 

[Fishrrman]

Sometimes... sometimes... it's "just that particular drive".
One drive won't work, while others will.

Have you tried any OTHER USB drives?

 

[macrlz9]

Sometimes... sometimes... it's "just that particular drive".
One drive won't work, while others will.

Have you tried any OTHER USB drives?

This particular drive has lived as a usb macOS installer and works just fine that way so I didn’t really think of trying a different drive... I will give that a try and report back!

 

[macrlz9]

Just realized I forgot to report back. Yes! I tried an old spinning USB2 hard drive and it worked just fine. Go figure! The flash drive I was trying to use works fine as a bootable macOS installer, just won’t boot if macOS is installed onto IT. Weird!

 

[gilby101]

Just realized I forgot to report back. Yes! I tried an old spinning USB2 hard drive and it worked just fine. Go figure! The flash drive I was trying to use works fine as a bootable macOS installer, just won’t boot if macOS is installed onto IT. Weird!

Power is my guess. The drive will be much more active as boot disk (compared with just an installer) and that consumes more power. And the use of a converter dongle doesn't help.

 

[Gravydog316]

is the external drive chosen by SysPrefs as a Time Machine backup volume?