warning: MT mapping is not completely referenced.

I did "diskutil resetFusion", then completely reinstalled Catalina. After initial reboot and restored my account via Time Machine (did not restore application or other stuff), disk seems ok. First Aid on either Fusion or Container were good. But after I install some applications, including Office and Parallels, I got 3 of these warning messages. I did not use Boot Camp. I thought Boot Camp might be the issue. Without doing much on my iMac, I got 8 of these warning messages. My 2017 iMac runs on Catalina. Please don't tell me to upgrade to Monterey which has big issue with external HD (loss of data and cannot not be mounted again).

The warning message is very much the same as someone posted two years ago. Maybe someone had a fix.

iMac 27″ 5K, macOS 10.15

Posted on Oct 15, 2022 11:59 PM

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4 replies

Dorain1

Community Specialist

Oct 17, 2022 11:29 AM in response to dz2010

Hey dz2010,

We'd like to have you take a look at this article: How to fix split Fusion Drive - Apple Support and see if the steps found here will help out.

If you still need assistance, reach back out.

Take care!

mario49

Community Specialist

Oct 17, 2022 12:14 PM in response to dz2010

Hey dz2010,

Thank you for using the Apple Support Community. Due to the nature of your issue, you may find more information by contacting Apple Support directly using the link below.

Contact Apple Support

Take care.

dz2010 Author

Level 1

18 points

Oct 17, 2022 12:04 PM in response to Dorain1

Thank you. I followed exactly these steps. No warning initially. As I use the machines, I got more and more warnings, initially 3 warning, grew to 8, then grew to 12 lately.

Turn on your Mac, then immediately press and hold Command-R to start up from macOS Recovery. Release the keys when you see the Apple logo or spinning globe.
When you see the macOS Utilities window, choose Utilities > Terminal from the menu bar.
Type diskutil resetFusion in the Terminal window, then press Return.
Type Yes (with a capital Y) when prompted, then press Return.
When Terminal indicates that the operation was successful, quit Terminal to return to the macOS Utilities window.
Choose Reinstall macOS, then follow the onscreen instructions to reinstall the Mac operating system. Your Mac restarts from your Fusion Drive when done.

dz2010 Author

Level 1

18 points

Oct 21, 2022 10:36 PM in response to mario49

Update. I took my iMac to apple store for troubleshooting after talking to Apple Support. After four days, the problem is still not resolved. The technical person just ran diagnostics and reported no issue found. He did not even check warning messages in FirstAid in disktutil, until I showed him these messages in the recovery mode. It is kind of wasting my time. I took my iMac back. Problem is not resolved. I did another fresh install again, and warning is still there.

I booted the machine off Mohave, and guess what? FirstAid in diskutil does NOT report these warning. I will keep monitoring when these warning messages will have negative impact on performance.

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warning: MT mapping is not completely referenced.