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User profile for user: mmabale
mmabale Author
User level: Level 1
14 points

After Big Sur install, iMac went from 4TB of HD space to only 121GB SSD.

I recently got the no access/do not enter symbol on my 2014 27" iMac. My only resolution was to re-install the OS. I was forced to install Big Sur. But now it looks like the OS is only using the SSD storage. I believe my 2014 Mac had a combination of SSD and non-SSD drives. So my iMac storage went from a total of 4TB to 121GB. Can I fix this? How can I revert to older OS to be able to use my full disk space?

iMac 27″, macOS 11.6

Posted on Sep 21, 2021 5:14 PM

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User profile for user: Allan Jones
Allan Jones
User level: Level 9
69,440 points

Posted on Sep 21, 2021 5:17 PM

First, use this article to see if your Fusion drive has "split":


How to fix a split Fusion Drive - Apple Support


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User profile for user: mmabale
mmabale Author
User level: Level 1
14 points

Sep 21, 2021 9:23 PM in response to Allan Jones

Thank you for the prompt reply, Allan.

I followed the instructions for running the diskutil from the terminal.


One thing that was different in my situation is that the rotational drive does not even show up at all, only the 121GB SSD.


I ran resetFusion anyway and got this:

"Error: -69760: Unable to write to the last block of the device"

My cursory search in the forums suggests there might be a physical problem with the SATA cable to the rotational drive(???)

That sounds like a hardware issue that I'm not equipped to fix.





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After Big Sur install, iMac went from 4TB of HD space to only 121GB SSD.

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