Downgraded from Catalina to Mojave...what is this?

ghsNick

macrumors 68030
Original poster
May 25, 2010
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I downloaded Catalina...and it caused issues with my iTunes library, so I downgraded to Mojave from a Time Machine Backup.

Now, I see this weird "Macintosh HD - Data" information when looking at my HD. It appears it was created during my Catalina upgrade?

Is there any way to remove it?
 

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randomgeeza

macrumors 6502
Aug 12, 2014
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United Kingdom
It's how Apple now lists the drives. System Folders are now secured, preventing any changes in there. Whereas your Data Partition is writable. It's all a little convoluted but it is normal. I'm sure someone on here will be able to explain it better than I have. What I can tell you is... "Do not remove it!".
 

Weaselboy

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Jan 23, 2005
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California
Catalina splits of the drive like that. Option key boot to your TM backup then launch Disk Utility. The set it to Show all devices. Then select the drive itself at the very top like in my screenshot and erase the drive back to one volume. Then restore your TM backup of Mojave and you should be all set back to one volume.
 

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ghsNick

macrumors 68030
Original poster
May 25, 2010
2,672
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Catalina splits of the drive like that. Option key boot to your TM backup then launch Disk Utility. The set it to Show all devices. Then select tjhe drive itself at the very top like in my screenshot and erase the drive back to one volume. Then restore your TM backup of Mojave and you should be all set back to one volume.
Thanks! That's working...but now to my new issue.

I have a "Security Update" that it wants me to do. After I click on it and restart my computer...I see this error. Which then makes me start up using Macintosh HD.

How do I install the update properly? I feel like my computer is being funky since I downgraded from Catalina.
 

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ghsNick

macrumors 68030
Original poster
May 25, 2010
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Try a command-option-r boot to Internet recovery, the use Disk Utility to run First Aid in the drive. See if that helps.
Did that...it ran successfully. It still doesn't work.

Very frustrating that I have this security update and can't apply it.