Time Machine Backups Failing: disk image ejected or disconnected

Issue: TM backups keep failing after a few minutes; error report ‘The backup disk image was ejected or disconnected from your Mac while backing up.’

System: Sequoia client, Dragonfish on NAS, using SMB.

Fix attempts:
Scale
*Reset SMB connection, tried both basic and multi user TM.
*Checked all SMB settings are per this
*Created new dataset for TM.

Sequoia Client
*Excluded sparse bundle from Spotlight.
*Set TM dataset to auto mount on login.
*Turned off MacOS firewall.

I’ve searched for issues reported with MacOS Sequoia TM backups on Dragonfish, but could not find anything. I accept it’s my fault for updating to Sequoia and Dragonfish within the same week without checking if TM was still working.

I’m out of my depth now as I only set all this up by following step-by-step instructions. I knew troubleshooting would be my downfall for my home set up. Is there something fundamental I’m overlooking to fix this?

Thank you, in advance.

Same for me here, waiting for the fix!

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I don’t know what your problem is, however, just so you know, works great on Dragonfish for me but I am still Sonoma as I don’t install .0 releases of software (Sequoia).

A quick search leads me to this:

The OP says wireless, but it applies to wired as there are plenty of other posts about this on the Apple discussion groups that are wired. Here’s one of those:

https://discussions.apple.com/thread/255762044?sortBy=rank

That’s for Synology users, but almost certainly applies to Truenas also as the first link mentions nothing about Synology. Sounds like a Sequoia issue. You may or may not have luck deleting your backup and starting over. It’s the pain of any .0 release of software most likely. My suggestion has been and will always be, never load the first version of any software.

Maybe someone else has found a workaround, don’t know, but it will be many months before I update my Mac (waiting for at least 15.2) so can’t really provide a solution at this time. You have tied the most likely solutions already.

If worth anything, here’s my share setup on Dragonfish, not much there:

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Thank you both.

Your Dragonfish setup was helpful, same as mine so I can rule that out.

Your first link mentioned Lulu may be a/the culprit. I disabled MacOS firewall, but not that. I’ve also noticed 15.0.1

I’ll try again with the OS update. If that fails, I’ll try again with Lulu disabled.

And I’ll never install .0 releases in future.

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I don’t see any issues with MacOS sequoia (granted I run the beta train). That said, 3rd party security software can and will often break OS behavior and so you may want to ask yourself whether you truly need it (often security software itself can become an attack vector). MacOS already has a firewall. I don’t see a purpose to a second firewall.

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Firewall on; Lulu off: still fails with the same error.
Firewall off; Lulu off: backup complete.

Still unsure why, but I’m relieved it’s backing up.

Ty, all, for helping with this.

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Same with me. I upgraded to 15.0.1 and the issue remains

Had the same behaviour here - from what I could find looks like this is an Apple specific issue with 15.0.1. Any sort of firewall (even the built-in Apple OS one) disconnects the backup process eventually.

Only way I can get backups running again is to disable the built-in firewall for now.

Many other users having the same issue - helpful thread and feedback/bug report link here.

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Is it Intel or Apple Silicon in your case?

My observations from using Time Machine for quite a while with Truenas as the traget:

I have also seen this message with Sonoma sometimes but only after waking up my M1 Mac mini from its kind of sleep. (The machine seems to have perfected the Power Nap feature. It seems to be sleeping but when I wake it up my RSS reader is up to date and it has done some time machine backups.)

Normal backups when the machine is fully awake always work fine.

The behaviour is also the same after upgrading it to Sequoia.

Some older versions of MacOS sometimes had problems when you had two connections with the same server with different users.
For example myusername was connected to some data share.
Time Machine had its own user TimeMachine for its share.
Then quite often there was some message like “Couldn’t mount Time Machine” when the scheduled backup was supposed to start.
Not being connected to data share backups always worked.

However I haven’t seen this for quite a while now. Apple seems to have fixed this.

M1 silicon for me.

Disabling the Firewall solved it for me. But I don’t like the solution.

It is indeed the mac firewall, possibly updated security protocols. Adding TimeMachine under options solved the issue for me and I am keeping the firewall running as well as Little Snitch. Thank you OP and rahidehzani.

How did you manage the firewall TM exception?

I added TM under options and ‘allow all connections’, but same error. Still working with Mac firewall completely off…

This is what I have on Sequoia, fwiw, just tested on my M1 and it only works on my Intel-based machine.

Thanks for testing both! Helpful to know im not missing something on my M1.