Not able to choose new external SSD as startup disk

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30 points

Not able to choose new external SSD as startup disk

This question was raised, and answered, on Aug. 15, 2018. I have the same question - with a twist.

I added an external Samsung T5 SSD to my Late 2012 iMac running macOS Mojave v. 10.14.2, formatted the SSD using Disk Utility with Mac OS Extended (Journaled) selected, and cloned the boot drive to it using Carbon Copy Cloner.

Upon completion of the cloning, I tried to select the SSD in Startup Disk System Preferences, but it was not there to select as you can see here:

I rebooted and, using Startup Manager, was able to select the SSD and boot from it - resulting in the expected performance increases. Not wanting to have to resort to Startup Manager every time, I tried to select the SSD in Startup Disk, but it still does not appear there. Finding the previous conversation mentioned above, I checked to confirm that I had selected Mac OS Extended (Journaled) when I formatted the SSD. This is where it gets strange.

As you can see below, Disk Utility shows the SSD is formatted Mac OS Extended (Journaled):

However, the Storage screen in System Information indicates that, while the File System for the Mac HD volume on it is Journaled HFS+, the Partition Map Type of the Physical Drive is MBR (Master Boot Record) - as seen here:

The USB screen in System information confirms that information:

What am I missing?

iMac Line (2012 and Later)

Posted on Jan 14, 2019 7:30 AM

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Answer 1

steveald Author

Level 1

30 points

Jan 14, 2019 8:04 AM in response to dialabrain

So, when I originally formatted the SSD, I was only looking at - and reformatted - the volume contained on it, not the device itself. Following your instructions, I now see the Erase function adds a Scheme setting when the SSD is selected - which I can change from Master Boot Record to GUID Partition Map as seen here:

Thanks! I'll give that a shot.

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Answer 2

steveald Author

Level 1

30 points

Jan 15, 2019 5:50 AM in response to dialabrain

That did the trick.

Another sign that it worked was the fact that, after it was done cloning, Carbon Copy Cloner asked if I wanted to create a Recovery Partition - which it did not do the first time. (Though that may have been more related to the fact that, the first time, CCC needed Privacy settings changed, which quit the app. So it wasn't running when it did the backup.)

Now I just need to switch my Time Machine backup to the new drive and decide what to do with the contents of the old internal drive.

Thanks again.

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