Fusion data structures are invalid

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vastunghia Author

Level 1

17 points

Fusion data structures are invalid

So today, all of a sudden, strange symptoms appeared on my new (purchased last December) 21.5-in 2019 iMac , such as

Some apps just won't load (I click them in the Dock, but nothing happens -- and Activity Monitor does not show any trace of them)
Some apps seem to load at first, but then (before showing their GUI) they appear as "not responding" in the Activity Monitor -- and they kick the CPU usage to ~50%, slowly eating up RAM and keeping accessing hard drive (one of these apps, in roughly 1 hour, progressively ate some 8 GB of RAM and accessed more than 150 GB of files on hard drives according to Activity Monitor, before pushing the OS into a kernel panic)
Mail.app says that there is something corrupted in mail boxes data, and that it needs to repair them, but then gets stuck in a loop of "click Exit to repair" > "data is corrupted" > "click Exit to repair" > and so on and so forth.
Just browsing through folders in Finder sometimes triggers the rainbow spinning wheel, and I have to wait for a few minutes before gaining back control.
Other apps just work (like Safari, for instance).

So I decided to run a disk check in Disk Utility, and this is what I'm getting:

[...]

error [...] fusion_mid_tree: bin: invalid o_cksum [...]

Fusion data structures are invalid.

The volume /dev/rdisk2s1 could not be verified completely.

[...]

I rebooted into Recovery Mode, performed the same check, but was thrown the same error message. No option is presented to fix the problem.

I also tried the Diagnostics tool at boot-up, but it failed at finding / reporting the issue.

Luckily enough, it seems that I am still able to boot normally (tried Safe Mode as well, but symptoms are still there) and was able (apparently! Fingers crossed) to perform complete refresh of Time Machine back-up on an external drive that I use for this purpose.

Unfortunately, the iMac is not usable.

So I might be in the position to reformat the Macintosh HD, hoping that this will fix the problem, and then restore all of my apps and data via Time Machine backups. Only, I'm afraid that the issue I'm facing is related to some sort of hardware (disk) failure, and that I will be wasting my time.

Any clue?

Thanks a lot

Sergio

iMac 21.5", macOS 10.15

Posted on May 10, 2020 9:01 AM

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Answer 1

Top-ranking reply

vastunghia Author

Level 1

17 points

May 10, 2020 1:55 PM in response to BDAqua

Thanks a lot for your comments.

So I booted from external TM drive, fired up Disk Util, and formatted Macintosh HD.

Formatting went apparently fine, but running the disk check still reported the same issue (“Fusion data structures are invalid“).

So, just as a desperate move, I decided to test how a clean reinstall of Catalina would go — and of course it went bad, ending up in errors (console log read “disk29s1 cannot be transformed into APFS, so you cannot install MacOS on it“... disk*29*???).

Then I rebooted again from TM external drive, and played a bit more with Disk Util. I don’t know exactly how, but I ended up with a split Fusion drive (namely, SSD and HDD drive separate from each other)... Bingo!

I formatted both of them, followed Apple’s instructions for re-uniting them in a single Fusion drive, and... voilà! A brand new Fusion drive which passes all of Disk Util’s tests!

Currently I’m in the process of restoring my last backup from TM... should take somewhere between 6 and 18 hours I think.

Fingers crossed (and thank you again). Will let you know how this ends (and will run disk checks from time to time, anyway... very suspicious re: hardware malfunctions).

Sergio

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Answer 2

babowa

Level 9

78,429 points

May 10, 2020 3:46 PM in response to vastunghia

I would recommend that, in a few years, when you are ready for another Mac, you avoid anything with a fusion drive.

Additionally, those fusion drives are small (fast) SSDs, but, if you got the default configuration, super slow 5400 rpm spinning drives for the HD which means that most anything it does is going to be slow. I don't know why this combo is still being offered - I would not buy it.

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Answer 3

vastunghia Author

Level 1

17 points

May 12, 2020 11:11 PM in response to vastunghia

So yes, just to confirm that the back-up was successfully restored from TM, and that everything works fine! It was 24 hours of terror... but with a happy ending after all!

Thanks for the support.

Sergio

Ps: when I purchased the Mac, I was a bit skeptical about Fusion drives, and I knew that APFS is still a bit young... guess somehow this experience is confirming my doubts. Too bad a 100% SSD could not fit my budget. Oh well. Keep backing up, and carry on!

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Answer 4

BDAqua

Level 10

245,393 points

May 10, 2020 9:08 AM in response to vastunghia

Sergio, yes you're on course with reformat & restore using TM, but for such a new Mac U'd suspect a possible hardware problem, especially if it happens again.

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