Cannot boot in Monterey from external SSD

[Speed38]

My Mac is a 2015 iMac running Monterey and I believe my internal Fusion drive is showing its age.

I placed an OWC Mercury Electra 6G, 500GB SSD into an external USB HD enclosure, installed Monterey on it, booted from the OWC Mercury, then migrated my data from a TimeMachine backup.

Everything went perfectly until I tried to reboot after I migrated.

Reboots hang after about 10 seconds and the light on the external drive enclosure stops blinking. I tried two different enclosures with exactly the same results: The boot hangs after about 10 seconds. BTW - I reboot, and as soon as I hear the chime I hold down the Option key to get the choice of which of the two boot drives from which to boot.

Can anyone offer any suggestions I might try?

 

[Fred4]

My Mac is a 2015 iMac running Monterey and I believe my internal Fusion drive is showing its age.

I placed an OWC Mercury Electra 6G, 500GB SSD into an external USB HD enclosure, installed Monterey on it, booted from the OWC Mercury, then migrated my data from a TimeMachine backup.

Everything went perfectly until I tried to reboot after I migrated.

Reboots hang after about 10 seconds and the light on the external drive enclosure stops blinking. I tried two different enclosures with exactly the same results: The boot hangs after about 10 seconds. BTW - I reboot, and as soon as I hear the chime I hold down the Option key to get the choice of which of the two boot drives from which to boot.

Can anyone offer any suggestions I might try?

Google OpenCore, I'm running NVME drives on all of my Mac Pros, and they normally act like external drives, even though they are internal on the PCI bus. OpenCore makes using them as internal hard drives possible. It may work for your situation, it's worth a try.

 

[Speed38]

Thanks so much for replying. While waiting for an answer, I continued my search and found the solution here:

How to Install macOS Monterey on External Hard Drive [4 Steps]

By installing macOS Monterey on an external hard drive, you can keep your main operating system intact and switch between them with ease.

www.macgasm.net

Where all the other advice is to format the drive on which Monterey is to be installed as AFPS, this site advises NOT to do so and their advice worked perfectly.