macOS CatalinA -Who knows this message (hard disk utility first aid) - Warning: MT mapping is not completely referenced?

After I can't upload a link ScreenShot...

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Run first aid on "Container disk2"

The computer does not respond while the startup disk is being checked.

Check storage system
Use live mode.
Execute fsckapfs -n -x -l / dev / disk0s2
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.
Checking volume.
Checking the APFS volume superblock.
The volume Macintosh HD - Data was formatted by diskmanagementd (1412.141.1) and last modified by apfskext (1412.141.1).
Checking the object map.
Checking the snapshot metadata tree.
Checking the snapshot metadata.
Checking snapshot 1 of 2 (com.apple.TimeMachine.2020-07-29-150921.local)
Checking snapshot 2 of 2 (com.apple.TimeMachine.2020-07-29-170616.local)
Checking the extent ref tree.
Checking the fsroot tree.
Checking volume.
Checking the APFS volume superblock.
The volume Preboot was formatted by diskmanagementd (1412.141.1) and last modified by apfskext (1412.141.1).
Checking the object map.
Checking the snapshot metadata tree.
Checking the snapshot metadata.
Checking the extent ref tree.
Checking the fsroot tree.
Checking volume.
Checking the APFS volume superblock.
The volume recovery was formatted by diskmanagementd (1412.141.1) and last modified by apfskext (1412.141.1).
Checking the object map.
Checking the snapshot metadata tree.
Checking the snapshot metadata.
Checking the extent ref tree.
Checking the fsroot tree.
Checking volume.
Checking the APFS volume superblock.
The volume VM was formatted by diskmanagementd (1412.141.1) and last modified by apfskext (1412.141.1).
Checking the object map.
Checking the snapshot metadata tree.
Checking the snapshot metadata.
Checking the extent ref tree.
Checking the fsroot tree.
Checking volume.
Checking the APFS volume superblock.
The volume Macintosh HD was formatted by diskmanagementd (1412.141.1) and last modified by apfskext (1412.141.1).
Checking the object map.
Checking the snapshot metadata tree.
Checking the snapshot metadata.
Checking snapshot 1 of 2 (com.apple.TimeMachine.2020-07-29-150921.local)
Checking snapshot 2 of 2 (com.apple.TimeMachine.2020-07-29-170616.local)
Checking the extent ref tree.
Checking the fsroot tree.
Verifying allocated space.
warning: MT mapping (0x4000004048a40 -> 0x12ceb94, 164, C) is not completely referenced
warning: MT mapping (0x4000004048bb8 -> 0x12cecfa, 344, C) is not completely referenced
warning: MT mapping (0x4000004048dff -> 0x12cef11, 106, C) is not completely referenced
warning: MT mapping (0x40000040dd7fd -> 0x1354f87, 32, C) is not completely referenced
warning: MT mapping (0x40000040f24b7 -> 0xa5ef4d, 1, C) is not completely referenced
warning: MT mapping (0x40000040f8294 -> 0x850e9a, 2, C) is not completely referenced
warning: MT mapping (0x40000040fff30 -> 0x137268b, 164, C) is not completely referenced
warning: MT mapping (0x40000041000a8 -> 0x13727f1, 190, C) is not completely referenced
warning: MT mapping (0x40000041075f7 -> 0xa5ebe9, 1, C) is not completely referenced
warning: MT mapping (0x400000410760b -> 0x1377f47, 8, C) is not completely referenced
warning: MT mapping (0x400000410761c -> 0xa5ebf1, 1, C) is not completely referenced
warning: MT mapping (0x400000410761d -> 0x1377f57, 8, C) is not completely referenced
warning: MT mapping (0x4000004107625 -> 0xa5ebfe, 1, C) is not completely referenced
warning: MT mapping (0x4000004107626 -> 0x1377f5f, 8, C) is not completely referenced
warning: MT mapping (0x4000004107aec -> 0x13782f6, 24, C) is not completely referenced
warning: MT mapping (0x4000004107b05 -> 0x137830e, 32, C) is not completely referenced
warning: MT mapping (0x4000004107b26 -> 0x137832e, 24, C) is not completely referenced
warning: MT mapping (0x4000004107b3f -> 0x1378346, 32, C) is not completely referenced
warning: MT mapping (0x400000410a877 -> 0xd296fd, 6, C) is not completely referenced
The volume / dev / disk0s2 appears to be OK.
Storage system check exit code is 0.

Operation successful.

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what is to blame for the mistake?

I too am curious what is to blame for this warning and poor reference. It appears I have the exact same message in first aid. Also, I have had two start up disc failures 7 days apart, on top of some other strange things (like photos not responding). Current solutions in between startup disc failures were to complete first aid, reset SMC, reset NVRAM, and ultimately reformat volume and reinstall (clean) OS 10.15.x. I found that recovering from time machine ate up about 250gb of my 1tb hard drive. I did not think to check first aid on volume until after initial time machine recovery. I am concerned one or both parts of the fusion hard drive are failing.

Has anyone ever helped you with this? I also get these mapping errors and like you said it's next to impossible to find any good intel about it on google.

Can someone please advise if they know anything about this. I've been dealing with it for months.

Running First Aid on “Container disk2”

Verifying the startup volume will cause this computer to stop responding.

Verifying storage system
Using live mode.
Performing fsckapfs -n -x -l /dev/disk1s2
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.
Checking volume.
Checking the APFS volume superblock.
The volume Macintosh HD - Data was formatted by diskmanagementd (1412.141.1) and last modified by apfskext (1412.141.1).
Checking the object map.
Checking the snapshot metadata tree.
Checking the snapshot metadata.
warning: MT mapping (0x40000002d013b -> 0x4fdcef, 1, C) is not completely referenced
warning: MT mapping (0x400000037350d -> 0x11657e, 1, C) is not completely referenced
warning: MT mapping (0x400000037350e -> 0x4083da, 3, C) is not completely referenced
warning: MT mapping (0x4000000373516 -> 0x4083e0, 3, C) is not completely referenced
warning: MT mapping (0x400000049a588 -> 0x4f8062, 1, C) is not completely referenced
warning: MT mapping (0x40000011b6317 -> 0x4087a8, 3, C) is not completely referenced
warning: MT mapping (0x40000011b6cdd -> 0x408b91, 3, C) is not completely referenced
warning: MT mapping (0x40000011b6ce3 -> 0x2c011b, 4, C) is not completely referenced
warning: MT mapping (0x40000011b6ce7 -> 0x42087a, 2, C) is not completely referenced
warning: MT mapping (0x40000011b6cfb -> 0x2c0106, 4, C) is not completely referenced
warning: MT mapping (0x40000011b6d6e -> 0x2c0123, 4, C) is not completely referenced
warning: MT mapping (0x40000011b6df5 -> 0x4087b4, 3, C) is not completely referenced
warning: MT mapping (0x40000011b6e03 -> 0x408b8b, 3, C) is not completely referenced
warning: MT mapping (0x40000011b70f2 -> 0x408ba6, 3, C) is not completely referenced
warning: MT mapping (0x40000011b726b -> 0x2c013f, 4, C) is not completely referenced
warning: MT mapping (0x40000011b7283 -> 0x2c013b, 4, C) is not completely referenced
warning: MT mapping (0x40000011b728f -> 0x2c0133, 4, C) is not completely referenced
warning: MT mapping (0x40000011b729b -> 0x2c012f, 4, C) is not completely referenced
warning: MT mapping (0x40000011b72a4 -> 0x2c0137, 4, C) is not completely referenced
warning: MT mapping (0x40000012848a6 -> 0x247574, 1, C) is not completely referenced
warning: MT mapping (0x40000020003ed -> 0x33274a, 1, C) is not completely referenced
warning: MT mapping (0x4000002002087 -> 0x3362fd, 2, C) is not completely referenced
warning: MT mapping (0x4000002002225 -> 0x3363b3, 2, C) is not completely referenced
warning: MT mapping (0x4000002029a00 -> 0x1a6735, 1, C) is not completely referenced
warning: MT mapping (0x40000022493f1 -> 0x259c0b, 2, C) is not completely referenced
warning: MT mapping (0x4000002291309 -> 0x18754c, 1, C) is not completely referenced
warning: MT mapping (0x400000229dfdc -> 0x498d00, 1, C) is not completely referenced
warning: MT mapping (0x400000229dfdf -> 0x498d01, 1, C) is not completely referenced
warning: MT mapping (0x400000229dfe0 -> 0x25992f, 2, C) is not completely referenced
warning: MT mapping (0x40000025c065b -> 0x3f94eb, 1, C) is not completely referenced
warning: MT mapping (0x40000026604e9 -> 0x49ef38, 1, C) is not completely referenced
warning: MT mapping (0x40000026604ee -> 0x49ef3d, 1, C) is not completely referenced
warning: MT mapping (0x4000002663fab -> 0x4b2fb3, 1, C) is not completely referenced
warning: MT mapping (0x40000028577a9 -> 0x388406, 1, C) is not completely referenced
warning: MT mapping (0x400000285d2ab -> 0x38de3b, 1, C) is not completely referenced
warning: MT mapping (0x400000285d2b0 -> 0x38de40, 1, C) is not completely referenced
warning: MT mapping (0x400000285d2b1 -> 0x25c8ad, 4, C) is not completely referenced
warning: MT mapping (0x400000293743c -> 0x19bb67, 1, C) is not completely referenced
warning: MT mapping (0x40000029b8e92 -> 0x4bace2, 1, C) is not completely referenced
warning: MT mapping (0x40000029edc07 -> 0x1eb282, 1, C) is not completely referenced
warning: MT mapping (0x4000002abb035 -> 0x1ea961, 1, C) is not completely referenced
warning: MT mapping (0x4000002abc8c5 -> 0x1ecb21, 1, C) is not completely referenced
warning: MT mapping (0x4000002ae4df7 -> 0x62e635, 1, C) is not completely referenced
warning: MT mapping (0x4000002b9e962 -> 0x4a5232, 1, C) is not completely referenced
warning: MT mapping (0x4000002ba36bd -> 0x1f24a5, 1, C) is not completely referenced
warning: MT mapping (0x4000002ba36be -> 0x1dd22e, 4, C) is not completely referenced
warning: MT mapping (0x4000002bb59e2 -> 0x1a4d57, 1, C) is not completely referenced
warning: MT mapping (0x4000002cdc5a9 -> 0x25ebc4, 1, C) is not completely referenced
warning: MT mapping (0x4000002cf1ab9 -> 0x1a1f42, 1, C) is not completely referenced
warning: MT mapping (0x4000002cfb8e3 -> 0x1ee246, 1, C) is not completely referenced
Too many warnings of this type generated; suppressing subsequent ones.
The volume /dev/disk1s2 appears to be OK.
Storage system check exit code is 0.

Operation successful.

I have run Disk Utility on fresh install of Catalina (done a week ago) after disk wipe on the Fusion drive of an iMac and I get the same crap, a bunch of: warning: MT mapping (****************) is not completely referenced

My last iMac is quite old (and its Disk Utility is not quite as crippled or dumbed down) and Disk Utility also always produced tons of problems with references that never went away and never seemed related to any known problem (because there weren't any). I too would like to know what gives. We have a critical utility that seemingly does the bare minimum and yet finds problems (my assumption is that they are) of little consequence except they are a perpetual annoyance and therefore should be sufficiently explained or somehow done away with.

Count me in with the same issue. And, I too suspect the fusion drive is at fault. I've had to rebuild my hard drive (3 TB Fusion) twice on a 2019 iMac 27" 5k model fully loaded. This is complete unacceptable so I'm taking it back to Apple under AppleCare and insisting on a complete replacement of the 3 TB Fusion drive. Disk First Aid, and the troublesome APFS/containers confusion, always reports this error. How do I know there is a problem? Finder slows to a complete crawl...beachballing...the computer becomes unusable. Couple in "snapshots" and "Time Machine" either capturing the bad blocks or replicating them on restores, and I'm left praying for Steve Jobs incarnation, you know, when Apple "just worked."

Trying to spread the word here. I was having this same issue. After a lot of trial and error and searching online, I followed the steps on this Apple support page and it completely fixed the issues I was having with my fusion drive: https://support.apple.com/en-us/HT207584

It was super easy if you're running Mojave or later. Literally just one command in terminal!

I've had this error for over a year on Catalina, Big Sur, and now just checking on Monterey as well. I've been scanning for an answer to this for over a year and nothing so don't hold your breath. Best thing I can tell you is don't sweat it, everything is running fine. It would be nice if someone from Apple stepped up and answered this question considering how much money their customers put out to purchase a high end quality product. but Hey, what do I know.

It only fixes the problem with a shared Fusion drive, but not the error - This is Wrong: warning: MT mapping (0x4000000738f36 -> 0x66b00e, 24, C) is not completely referenced

I have had this error on my 2017 mid 5k iMac 27in. As another posted if you run the diskutil-verification tool you shouldn't see it BUT that does not excuse apple for not addressing this problem. The amount of $ we all spend you would think someone would of the common decency to post SOMETHING about this MT-Mapping problem that has been happening for two years now. Welcome to customer server 2021. No CSR's answer you and they have search engine algorithm's so jacked up because of the suppression tools it makes a simple search turn into a ready to throw out the window situation.

I'm also adding to this because I am having the exact same problems with a client's 2017 27" 5K iMac with a 3TB Fusion drive running Monterey 12.4. Apple needs to address this issue as I have scoured the web and this is the only legitimate forum I can find discussing this unsolved issue. I am loath to spend the time and the commensurate expense to the customer remerging a Fusion drive that isn't broken ( https://support.apple.com/en-us/HT207584 ), reinstalling the Mac OS, and restoring from Time Machine just to have the problem reappear as is suggested by some of the above posts. Come on Apple, make an effort to FIX THIS PROBLEM.

Found exact same problem with my Mac Mini 2014 - Monterey 2.4. No answer anywhere. Thank you Apple!

Same issue with my 2019 27" 5K iMac with a 1TB Fusion drive running Monterey 12.4

Found when looking why the computer keeps freezing and doesn’t seem to ever get rid anything from the memory (unable to start on recovery mode)

Same issue with a late 2014 iMac 27" running BigSur. The machine seems to run OK so far (bought it used), but when I run Disk First Aid seeing a large number of the:

warning: MT mapping (0x40000002d013b -> 0x4fdcef, 1, C) is not completely referenced warning: MT mapping (0x400000037350d -> 0x11657e, 1, C) is not completely referenced warning: MT mapping (0x400000037350e -> 0x4083da, 3, C) is not completely referenced ....

I could try reinstalling the system from scratch, but I might just want to swap out the Fusion drive for an SSD (which might be a pain), or just get an external SSD.

Not sure that is the correct way, but there is a YouTube Video about how to replace an internal drive: https://www.youtube.com/watch?v=YZv6hR3VgyY

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.

Same problem on TWO mac minis I just bought (Intels were on sale). Both have fusion drives. errors on the Container disk only.

Safe boot - same.

Recovery Disk Utility - same.

Reinstalled Mojave on both - same errors.

DiskDX says both fusion drives are fine.

Maybe it is Mirosoft Office items - I've read of problems with OneDrive and the notes that come with it (I don't use them but they were installed). Uninstalling them didn't help, however.

No solutions on the web so far.