What causes TimeMachine backups to fail on NAS devices?

Exactly the same here. Access to the NAS via Finder also not possible anymore:

Nothing has changed in my setup, except installing upgrade to 15.0.1. Since then I get this in the console:

Backing up to my Synology NAS, using Sequoia 15.0.1 (24A348), only works in Safe Mode.

15.1 with Firewall on + Little Snitch still does not working for me. It also says Drive disconnected sometimes and "in use" but it isn't.

After two failed migrations on 15.0.1 (I thought that it was my fault the first time …) I reverted the MBA M3 to Sonoma 14.7, and migrated again. TM works now, and I’ve created a usable sparse bundle from the new machine (as well as having two good ones in reserve from the old machine.

There are better ways to spend a weekend.

I have spoken to my firewall provider, and understand that 15.1 fixes the various firewall and network problems that were so freely given in 15.0.1. Lets hope that it’s soon and that they’re correct!  

I have the same setup on 4 x machines and it 15.1 is working fine, 3 x MacBook Pros and 1 x MacBook Air.

Little Snitch 6.1.2

I guess you could uninstall Little Snitch to check if it is that getting in the way?

Adrian.

I have the same NAS setup. My Time Machine backups (scheduled and manually invoked) have failed with the installation of the Sequoia 15.1.1 update, for a variety of reasons - eg: network connection dropped. They might progress a few MB, then fail. Was working perfectly before then, and there's not been any other changes to my NAS or network.

I have tried all of the above suggestions, and much more, but no go.

Whatever the security issue the update "fixed" was clearly some serious sh1t that it's broken other things in the process. I just wish they'd explain what it was they did - but I guess that'd help the bad guys...Meanwhile, hoping Mac's hard drive doesn't die anytime soon!

I have just updated three machines to 15.1.1 (avoided 15.1).

One is a mac mini 2018 intel, which has two LaCie drives attached for network time machine backup, the others are both MBA Mx laptops.

One of the MBAs was on 15.0.0 while the others were on 14.7.0. In that situation, I had various and many failures with the networked disks disappearing during a backup of the 15.0.0 machine. Also repeated failures of screen sharing to the mac mini.

With all machines on 15.1.1, those problems have stopped. I have run several backups from both laptops to the mini and screen sharing between all three works fine.

This has been a very unsatisfactory series of events, and I'm sure that it hasn't entirely gone away, especially as some NAS users are still having problems.

In conversation with an Apple person, I asked why they didn't have field testers (you or me) who could run through the non-standard setups that are likely to occur in abundance outside Cupertino. The response was that if I encounterd a failure, I could mail the logs, but there was no plan to introduce field testing of that kind. In the dim and distant, I worked on IBM MVS/370 -- IBM's standard policy seemed to be to ship buggy software, then let the users fix it and send the patches back to base for distribution round the world. It wasn't ideal, but it worked.

Apple, perhaps you could give it a thought. The Beta programme obviously didn't pick up this mess.

I have called Apple support twice since I first reported it on 03-Nov-24. They are in complete denial. This past weekend I spoke to a Senior Advisor instead of the first level support (Advisor) and he acknowledged that this is an Apple issue but he was completely un-interested in offering any solution or information. So, I wasted 2-3 hours trying to get more information and re-escalating this Apple MacOS bug. I find it baffling that they are not concerned about some form of bad interaction between the Firewall (or security) and another OS important function like TM.

I have made clear that it is not just Synology. My NAS is a My Cloud EX2 Ultra by WD also fails TM backups when the MacOS Firewall is on. More importantly, it also fails with a Seagate SDD attached directly to the MacBook Pro M1 I have. Turning off the Firewall causes BOTH to start working.

[Edited by Moderator]

So last night I managed to make the backup that had eluded me. If you've read my previous posts, I have an old Synology NAS and a new one. I had failed until turning off the firewall on 15.0.1 to make a backup on the old, which caused me to buy the new. 15.1 fixed the problem on the old, but I could not get it to work on the new one. Yesterday I made a new copy of the sparsebundle from the old on the new. That one I was able to back up to.

I don't know if this is a permanent fix. The copy was almost up to date, so the backup didn't need to be connected very long. When it failed before it would work for a while and then say "can't connect", which was wrong because it had been connected. I'm going to watch it for a week or two and backup to both machines.

It's possible that some of the problem is that 15.0.1 was bad and corrupted the backups. It may be that for some making a fresh backup will work.

Good luck to all of us (and Happy Thanksgiving to those in the US)

I've had the same problem too. Time Machine backups started to fail after upgrade to OS 15.0.1. Both on a network attached storage (NAS) device AND on a Mac Mini as backup destination.

On the Mac to be backed up (MacBook Pro M3, source), I went to Settings, then Time Machine, and removed the destination that was failing. But I could not add it again until I did the following.

Backup disks you can use with Time Machine - Apple Support

For backing up that Mac (source) to another Mac computer (destination): I went to Settings on the destination Mac, selected General, File sharing, added the destination device/folder, and then right clicked on the added device/folder, and selected “Share as a Time Machine backup destination,” then clicked OK.

Then on the Mac I wanted to backup from (source), I saw the external Mac destination for doing the backup. Add the new destination, choose to use the same backup device/folder as before, and let it do the next backup.

However, it failed again on the Mini as destination: "The network disk disconnected from your Mac while backing up".

The NAS I'm using is on an AirPort Extreme (old Apple device with USB connection to a 6TB hard drive). It very recently started failing backups too with the same error message as for the Mini as a destination.

Finally, I am running Bitdefender on both the M3 MacBook Pro and M1 Mini, BUT I have disabled its protection for Time Machine backups since that previously interfered with doing backups over the LAN (several years ago now).

I have not disabled the MacOS firewall in network settings on either the MBP or Mini.

To be clear, this is a problem with non-Apple firewalls, introduced by new code in 15.0.1. 

It’s not specific to a particular target system for a time machine network backup. 

It doesn’t matter what your target system is, or what your third-party firewall is. If you put 15.0.1 onto a machine that backs up to a target elsewhere on your network, then there is a very high likelihood that it will fail. 

If you turn off the firewall (or open specific ports) there is a very high likelihood that it will work again. 

There is a very high likelihood* that this has been caused by inadequate pre-release testing of 15.0.1. 

If you want to make the strength of your feelings known to Apple, do it here:

Feedback - macOS - Apple

*¿am I repeating myself?

I was having the same problems – TM backups to my Synology NAS failing midway (via samba and afps). I did as people suggested and disabled Lulu and macOS built-in firewall and the backup functionality did work, but I kept testing. I found that after permitting smbd AND Lulu as a process/application in the firewall settings, I was able then able to enable the firewall AND Lulu AND successfully perform a TM backup. I'll see how it stands over time, but I wanted to share in case others would like to try this solution and report back if it works for them, too.

On a separate issue, TM backups tend to fail if you lock the screen. Presumably, Apple's security autocrats decided this was dereliction of duty. The commandants insist we remain handcuffed to us computers during backups. Of course, anyone with an iota of understanding of human nature knows that people will do what is easiest – leave their computers unlocked and insecure. Self-defeating!

+1

Temporarily disabling the firewall and initiating the backup manually seems to be the only reliable workaround.