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What causes TimeMachine backups to fail on NAS devices?

The newest fun part: with the latest update the network connections with enabled Firewall are stable, but if you backup your Mac with TimeMachine to a NAS device, the backup is no longer working. Stops between 200 and 400MB.




[Re-Titled by Moderator]

MacBook Pro 16″, macOS 15.0

Posted on Oct 4, 2024 4:35 AM

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Posted on Oct 5, 2024 6:29 AM

I back up to a Synology NAS using Time Machine and it worked yesterday and not today after 15.0.1 update

"The network disk disconnected from your Mac while backing up."


Mine gets to 0MB. But with a film playing off the same NAS during backup gets to 95 MB then goes to 'skipping'

96 replies

Oct 14, 2024 9:53 AM in response to NBT123

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!  

Nov 22, 2024 10:32 PM in response to Lundyfox

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!

Nov 23, 2024 5:52 AM in response to matthias260

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.

Oct 7, 2024 5:49 AM in response to matthias260

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.

Oct 19, 2024 1:35 AM in response to Nick-UK

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?


Oct 18, 2024 3:23 PM in response to matthias260

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!



What causes TimeMachine backups to fail on NAS devices?

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