How fix Fusion structure problems?

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How fix Fusion structure problems?

Yesterday Big Sur updates were automatically downloaded for installation during the night. When I started looked at my 2020 27" iMac this morning, that multi-language crash message displayed.

It took most of today trying learn what the problem is. I used DiskUtility to run First Aid from a different startup volume. First Aid failed because of Fusion structure problems.

I've tried many things from reading too many articles, but still not fixed.

I created a TechTool eDrive on an external hard drive. I can access all the volumes on the Fusion Drive, copy to/from them. But I can't start from the Fusion Drive.

I copied the DiskUtil First Aid log to a text file. But my iPad Pro can't access my iMac through my LAN. I need to create a second Big Sur startup disk and use the Migration app to move everything over. Then I'll post the log here.

Thankfully I have an iPad Pro to post here.

Until then, any workable suggestions?

Thanks,

Don

iMac 27″, 11.6

Posted on Apr 27, 2022 2:51 PM

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Answer 1

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Tesserax

Level 10

157,980 points

Apr 27, 2022 10:12 PM in response to DonLeckie

See if the following support article can help: How to fix a split Fusion Drive - Apple Support

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Answer 2

Tesserax

Level 10

157,980 points

Apr 28, 2022 7:00 PM in response to DonLeckie

Unfortunately, Storage does not provide you with the needed information to determine the state of your Mac's Fusion Drive. I suggest that you use the following command in the Terminal app: diskutil list

The image below would be the typical result for a Fusion Drive:

In this case:

/dev/disk1 (internal, physical) is the Fusion Drive's SSD component
/dev/disk2 (internal, physical) is the Fusion Drive's HDD component
/dev/disk3 (synthesized) is the Fusion Drive = SSD + HDD

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Answer 3

Ronasara

Level 6

15,519 points

Apr 28, 2022 9:59 AM in response to DonLeckie

I think that Tessera's suggestion is a good one. A Fusion Drive is a combination of two drives which work in unison as one drive. You have an older, slower mechanical HD and a smaller, fast SSD. It sounds to me as if the two drives are no longer functioning together as a fusion drive. Unfortunately, the only way to fix the problem is to reformat the drive and then do a Fusion Drive repair as spelled out. So, first do a backup of your data and then proceed with the repair.

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Answer 4

DonLeckie Author

Level 1

20 points

Apr 28, 2022 12:23 PM in response to Tesserax

I checked "About This Mac" > "Storage" and I see one drive called "Fusion Drive". So, accordingly to the above article the Fusion Drive is not split.

Guess I need a bottle of Burgundy and reformat the Fusion Drive and reinstall Big Sur.

When powering on my iMac, the Command-R always tries to connect to the Recovery on the Internet. Naturally, my iMac is not connected to the Internet yet. Since I cannot access the local Recovery, I'll try using TechTool's eDrive; but first I need to get a Big Sur Installer.

Thanks, all!

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Answer 5

DonLeckie Author

Level 1

20 points

Apr 27, 2022 7:23 PM in response to DonLeckie

Running First Aid on “BigSur” (disk2s12)

Repairing file system.

Volume was successfully unmounted.

Performing fsck_apfs -y -x /dev/rdisk2s12

Checking the container superblock.

Checking the fusion superblock.

Checking the EFI jumpstart record.

Checking the space manager.

Checking the space manager free queue trees.

Checking the object map.

Checking the Fusion data structures.

error: btn: invalid key order (98) oid 4480089 / oxid 0 / level 1 / flags 0x4

previous key: 0x000400001e727755

current key: 0x00040000167816c7

next key: 0x000400001d517d70

Fusion data structures are invalid.

The volume /dev/rdisk2s12 could not be verified completely.

File system check exit code is 8.

Restoring the original state found as mounted.

File system verify or repair failed. : (-69845)

Operation failed…

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Answer 6

DonLeckie Author

Level 1

20 points

Apr 28, 2022 12:32 PM in response to Ronasara

Please my response and image to Tessera.

Wish I could know what caused the Fusion data structures to have an invalid key order.

I'm considering an external SSD for the MacOS. Wish I had not selected the Fusion Drive. My 2020 iMac is slower than my Early 2008 MacPro both in processing and I/O. Oh well, that's progress! 😳

Thanks!

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Answer 7

DonLeckie Author

Level 1

20 points

Apr 29, 2022 7:18 AM in response to Tesserax

My Fusion Drive appears to be okay:

/dev/disk0 (internal, physical) is the Fusion Drive's HDD component
/dev/disk1 (internal, physical) is the Fusion Drive's SSD component
/dev/disk2 (synthesized) is the Fusion Drive = SSD + HDD

Using another startup drive, I can access files in all the volumes listed above. The issue is only when starting up from the Fusion Drive.

I created a new Big Sur bootable volume on an external drive. The Migration app copied the files from the old Big Sur volume on the internal drive. Now I can boot from the external drive. I'll reformat the internal drive, reinstall Big Sir on it and what happens.

Thanks!

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Answer 8

Tesserax

Level 10

157,980 points

Apr 29, 2022 9:57 AM in response to DonLeckie

Yes, it does appear that your Fusion Drive is intact. Thanks for providing the results of the diskutil list command. I see that you also created multiple additional volumes in your drive's APFS Container, which shouldn't be an issue related to this.

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Answer 9

Ronasara

Level 6

15,519 points

Apr 28, 2022 1:18 PM in response to DonLeckie

Most likely it is slower because it's working on the slower mechanical part of the HD. If it were connected to the SSD is would be much faster.

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