fsroot root tree is invalid

Hi I had the same problem. Following a method from a similar High Sierra question I solved mine (also "error: btn : invalid btn_tree.bt_key_count..."). Boot into Recovery with Command (⌘)-R, run Disk Utility, mount main drive, run First Aid on that drive. This did some repairs. Then a normal reboot, run First Aid again: error gone - there was a message about doing deferred repairs. Hope this helps for you too.

Repaired mine by going into single mode (command c) while restarting. I then did the fsck command /sbin/fsck -fy then enter. It ran a disk repair. Found a issue and repaired it. It’s actually the old old way of running disk utility. Not sure why it works. It’s suppose to be same thing.

I was having the same problem and this is how I had to fix it:

https://discussions.apple.com/thread/8564919?answerId=250086718022#250086718022

This worked for me (using Command S). Happy New Year!

HI Guys,

Not a noob (30+yrs Win,Mac); but haven't had any issues with any MacOS before now.

Running First Aid on “MyDriveName_3TB” (disk3s1)

Repairing file system.

Volume is already unmounted.

Performing fsck_apfs -y -x /dev/rdisk3s1

Checking the container superblock.

Checking the space manager.

Checking the space manager free queue trees.

Checking the object map.

Checking volume.

Checking the APFS volume superblock.

The volume MyDriveName_3TB was formatted by newfs_apfs (748.41.3) and last modified by apfs_kext compiled @ Jun 21 201.

Checking the object map.

Checking the snapshot metadata tree.

Checking the snapshot metadata.

Checking the extent ref tree.

Checking the fsroot tree.

error: (oid 0x404) apfs_root: btn: _omap_lookup_obj(0x404, 0x0): No such file or directory

fsroot tree is invalid.

The volume /dev/rdisk3s1 could not be verified completely.

Operation successful.

Now I get that APFS creates a APFS Container, called in this case disk3

but then it won't even mount the drive that has been working fine for a couple of years.

The difference here is that when I plugged the Drive, a WD My Passport Ultra 3TB, external drive into the newly updated Mojave OS the drive disappeared from the desktop. Running Disk Utility, trying to remount the drive looks like its going to start but then doesn't mount.

I run a 10TB external G-Drive Pro without any errors or problems of mounting, but it uses Extended Journaling.

Even my IPOD Nano appears!

Anyone have this issue or has resolved it successfully?

Many thanks if you can shed some light.

Steve

I thought this had worked for me, but the problem resurfaced as soon as I exited single-user mode and ran first aid on the disk again. I'll try it again and just immediately reboot afterward. Hopefully some combination will knock things into place. I saw several warnings about extents, so maybe there are some phantom extents or something that keep messing everything up. I'll try to pay attention to the difference in expected vs. actual extents as well...if it's always the same, that might be a hint.

Not working for me.

Still no luck

Happy it worked for ya! I was sooo happy when it worked for me. Happy new year!