Updating Big Sur, running from external SSD

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Level 1

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Updating Big Sur, running from external SSD

I am running Big Sur on a late 2015 iMac, and for space reasons had to start running from an external SSD. As others have noted, Big Sur has an issue with setting a new external boot drive and still defaults to booting from the internal drive unless you hold Option down when restarting.

The problem I am running into is when trying to update Big Sur. When it resets as part of the installation process, and I hold down the Option key and tell it which drive to boot from, it doesn't seem to have installed the update. I suspect it's not seeing where to install the update or not knowing to install it to the external drive. Not sure where to go from here but I've tried a number of things and I'm stumped.

I do see an alternative drive that shows up at boot time called "MacOs Installer" which I thought might be the updater, but all it does is restart over and over again and never properly boots or installs anything. Any ideas? Am I just missing some step in this process?

Posted on Apr 8, 2021 8:10 AM

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Answer 1

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Jack-19

Level 8

45,872 points

Apr 8, 2021 9:42 AM in response to LeeAtMg

Hi LeeAtMg,

You need to set the SSD as the default boot volume. There are two ways to do this:

Go to System Preferences > Startup Disk > Select the SSD > Restart.
Next time you boot the Mac, hold the "option" key. Then, select the SSD. Now, hold the "control" key. A spinning symbols should appear under the SSD name. Continue holding "control" and hit enter/return at the same time to confirm your choice.

If it still does not install the update, there is another problem.

Cheers,

Jack

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Answer 2

LeeAtMg Author

Level 1

4 points

Apr 21, 2021 8:06 AM in response to Jack-19

Jack;

Thanks. The second option did the trick.

I had tried the first - setting the startup disk - many times, but there appears to be a bug (maybe solved with the updates I could not install!) that caused Big Sur to fail to remember the correct startup disk and default to the internal HDD. I've seen many reports of this particular issue (and I can say it was the case for me - several occasions where files were missing, only to discover it was because the system had restarted and defaulted back to the internal drive.) For whatever reason, the second option did work and I was able to install the updates. Thanks very much for the help!

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Updating Big Sur, running from external SSD

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