Big Sur, Time Machine, SMB, umount, and Safari networking issue

I deleted the backup on my WD PR4100 per discussion above and then let TM build a new backup. The file format is now sparsebundle (was backupbundle). After a few hourly backups I think this issue is resolved for me. Umount was not spawned and Safari has not been problematic.

Just sampled the `umount` process when it was spinning and it’s basically blocked on `unmount` in `libsystem_kernel.dylib` which is simply the `unmount` syscall (thus whatever blocks is doing so in the kernel). I believe that the syscall is marked as non-interruptible which might explain why `kill -9` and friends don’t work. This could happen at the VFS layer but much more likely in the smbfs kext/driver.

I believe there were some changes in this kext for Big Sur (since they’ve also finally removed AFP) so I wouldn’t be surprised if some bug slipped in the first release (there were a bunch of `smbfs.kext` bugs already discovered during the betas too).

This problem now has a solution.

Disable Time Machine.

Delete your Time Machine backup from your NAS.

Re-enable Time Machine and let it create a new backup.

Problem solved. Mine hasn’t crashed since I did this a few months ago.

That's actually what sparked my idea to create a new one. I have two backups, my home one said the same thing like yours and recreated itself with the new APFS format. My other backup kept hanging and was thinking that using the old HFS format might be the issue.

I have the same problem with TimeMachine to my QNAP - umount hangs with 100% for one core and Chrome hangs when opening new tabs.

I erased my TM Backup and startet from scratch. This seems to have fixed the problem for the last 3 runs.

I experience exactly the same problem.

This helped me (as a turnaround): enter in "Activity Monitor": double click the process "umount" (which uses 100% CPU) and press button "Quit". The process "umount" stopped immediately and Safari resumed instantaneity to work.

Anyhow I believe it is an error of Big Sur and Safari and I hope for a fix in the next update of Big Sur.

Thank you.

This is anecdotal but I deleted my TM backup and created a new one and it seems to no longer be hanging. YMMV

I should note that my backup got updated to the new APFS format (sparsebundle to backbundle, or vice versa, I don’t recall) after TM threw an error about it having to prune all the backup history.

Since then I have also not been experiencing this issue anymore.

macOS 11.1 just came out. Hopefully it fixes this issue.

Umount takes 100% of cpu load and the machines slowly dies sometimes. Cursor is getting choppy and even a resatrt will not work, needs a hard shutdown on my Mac Book Pro 15" (2018). Sometimes just waiting solves the thing but it takes 10 or more minutes in which other tasks become very slow. Safari is also affected durin this time (in the first place I thought its the internet providers fault, but all other devices are conneting just fine).

Any news on this one besides turning of time machine?

I am having the same issues with my 2017 15" MBP connecting to SMB on my QNAP NAS, so I don't think it's Synology. Running Big Sur 11.1. My iMac Pro and iMac both work fine. Just the MBP.

I've turned off automatic backups for now, hopefully this is something that gets solved. For me, randomly the machine would lock up. Jittery and eventually locked cursor and need to hold power button for 10s to restart the machine. Everything else is dead.

I have deleted my old backup off my NAS and have just started again... let us see if that solves the issue! I will report back when the backup has finished and I've used it a bit next week.

Identical problem to mine and it fixed it.

Try this. Disable Time Machine for a day. Bet that fixes the problem. Then you’ll know.

Im giving you the fix to your problem

Almost same issue here, but from mac mini time machine share over smb. Affected are safari and chrome (not even loading start page), diskutility (won’t open), time machine config panel (open to select new time machine target hangs). All hanging with ‘unmount’ process eating one processor completely. In my case 30 minutes before return to ‘normal’ / timeout of process