macOS Tahoe 26.2 breaks Time Machine with Synology NAS

I installed Tahoe on my imac yesterday and now can't access my NAS at all in any way on that machine. And yes, it also broke Time Machine, which is backed up to Synology NAS. I didn't update my laptop, and it's fine. The Synology community forum reports problems with Tahoe installs going back to October. No one has reported any way to fix it.

@MrHoffman: Good questions!

I did report the panics, indeed. It seemed to be coming from SMB crashing, making watchdogs to not show up for over 90 seconds, and force a reboot by itself, IIRC.

DSM 7.3.2-86009 on a DS923+.

I did use one of those 2 links, but didn't see the other one, thanks, I'll check it out!

No VPN, no ant-malware...just plain brand new wiped Macbook Air M2 with latest Sequoia and a few things (Homebrew, Firefox, Apple Container, Rectangle, Ghostty, Spotify, Steam, Mailspring and that's pretty much it, I think).

Edit: the only thing I did NOT do from the Synology link for failed Time Machine is this: "Make sure your Mac is connected to your NAS via SMB3. To check this, in DSM, go to Resource Monitor > Connections. If it doesn't say SMB3, you may need to contact Apple for further assistance.". If I decide to try again (I disabled Time Machine for now), I'll check it.

Mac should not panic. What’s in the panic? If it’s all Apple with no kexts or such, report the SMB panic to Apple.

Which DSM? 7.2.2-72806? 7.3.2-86009? Something else?

Checked and verified these?

• https://kb.synology.com/en-us/DSM/tutorial/How_to_back_up_files_from_Mac_to_Synology_NAS_with_Time_Machine
• https://kb.synology.com/en-us/DSM/tutorial/Time_Machine_backup_failed

Safe Mode boot on Mac tested?

Any add-on VPNs, add-on anti-malware apps, add-on security apps, add-on firewall or networking apps including Little Snitch, or similar apps, installed?

Post an EtreCheck report, if that’s available.

I think 26.2 currupted my apfs. As my SMB share is backed by a ZFS mirror I doubt it is my underlying storage.

** Checking the object map.
warning: (oid 0x8e4814e) om: btn: invalid o_cksum (0x9001a80000000a)
   Object map is invalid.
** The volume /dev/rdisk5s1 with UUID <redacted> was found to be corrupt and cannot be repaired.

Thankfully I can at least mount the filesystem RO.

Now I had to create a new backup. My logs also spam the

TMDisk attrVolumeWithMountPoint failed (Permission denied).

Error, but the backup still works.

It is not first time i get my backup currupted. I am so annoyed. I will now start to do ZFS snapshots of my backup volume so I can roll back the next time apple currupts my backup ... -.-

Fully aware that it's not helpful, but backups to my Synology DS223j NAS work fine in Tahoe from two Macs in the house (the other three are still on Sequoia). My Mac has been on Tahoe since launch day and is on 26.2 now. The last backup to ehe NAS completed a few minutes ago.

Update: it continues to make my Macbook Air M2 (16GB) crash with kernel panic, related to SMB. Even on Sequoia (I downgraded). Could it be just that they changed something in their SMB implementation, on both OS versions? Or Synology maybe changed something in their SMB implementation? idk. I followed the official Synology doc for setting up a new shared Time Machine drive...and same thing.

To be continued (or not; I am likely to just dump Time Machine altogether!)...

I don't know if my issue is related, but since Tahoe 26.2, my Macbook Air crashes during Time Machine backups to my Synology NAS with some kernel panics related to SMB.