What causes TimeMachine backups to fail on NAS devices?

After upgrading to 15.1, Time Machine to my NAS is working properly.

Updated to 15.1, tried with and without firewall - but still failing for me :(

I've been using Time Machine to a QNAP NAS for years and once I upgraded to 15.0.1, it stopped working. I even wiped the backups from the NAS and set it up from scratch, but it won't even start the first backup. Disabling the Mac firewall does not resolve the problem.

So for the second day, after getting TM to work with the FW off, I tried to backup without turning it off. And it failed. I even added the TM app to the rules of FW to accept incoming connections. But that didn't work either, it said the external disc had disconnected. So I turned off FW off again just for TM and it worked perfectly. This is an error introduced by Apple in 15 or 15.0.1. I will have to turn on and off FW just to get TM to work - how annoying.

It appears it is not just TimeMachine backups to SMB shares. VPN's, RDP connections, DNS lookup requests, 3rd party network security products etc.

Suggest everyone uses the feedback tool on their Mac's and report the issue, that is what that tool is for.

Lets us hope an update fixes this quickly, I can imagine quite a few systems will be affected.

Adrian.

I bought a new M3 MBA, installed 15.0.1 and migrated an old Intel MBA to it. T-M backups failed. Rather than go the long haul route, I shall downgrade the M3 to Sonoma 14.7.1 and reinstall.

Meantime, I've reported this direct to Apple executive relations.

This isn't just NAS's. I have two Mac Mini's and an MacBook Air. The Air is a M2 running 15.0.1 on of the Mini's is a M2 running 15.0. The third Mini is the target and it is older. It is an i7 running 10.15.7. All it does is act as the target and has worked for years until this update. The 15.0 machine works fine the 15.0.1 machine, no dice. I have gone as far as completely reformatting the target drive and reconnecting the Air to it. The connection is initially made and the sparse bundle is created but then the backup goes into the abyss and I get a failure that says the remote disk disconnected.

I am yet to look into the firewall fix that people have been talking about but this as someone said is a complete dumpster fire. Apple has really dropped the ball with 15.0.1. That 15.0 machine isn't getting the update anytime soon.

To add my tuppence worth, it’s more than just backups.

if you search you will find it looks like the Mac’s ability (or lack of) to communicate properly with devices on a local network.

I’ve had issues with RDP connections to machines on my local LAN, VPN issues into my local LAN and have seen reports of app developers struggling to get their programs to pop the “allow access to local lan?” message and I’ve also seen reports of DNS queries failing if the DNS server is on the local LAN.

Agreed it is really terrible and shoddy testing on the part of Apple.

These are not budget devices we invest in and I expect a bug as big as this one to be caught so early in the testing process so as not to appear in the public release.

I have fed back to Apple with my diagnostic logs.

It’s not NAS specific. It’s actually a network communications problem when the internal or even third party firewall is enabled. For me it’s the MacOS internal firewall but I’ve been reading others have a problem with third party.

Reach out to the developer would be my suggestion. I had a problem with my VPN (VPN Unlimited) and they had a new version available via the App Store than what I was running from their website and problem was resolved.

I may have a clue about what the problem is.

I have an old Synology NAS DS213j. Under 15.01 I needed to turn off the firewall in order to make a backup. Somehow when I upgraded to 15.1 things worked. I though the bug went away.

But it scared me enough that I decided I should get a NAS that's not a decade old and can run modern software. So I bought a Synology DS224+ and installed it. I tried to backup using timemachine to it. It fails in the way everyone's been reporting. Turning off the firewall doesn't help. BTW 15.1 vs 15.1.1 doesn't make any difference.

There are two large differences between the working old machine and the new one. The new one is much faster. And the new one is running the 7 Synology OS where the old one is running the 6. I've done my best to use the same settings but in the new OS.

My guess is the bug has something to do with a timing error, and that turning off the firewall perturbs the timing enough that it doesn't appear for some people.

I'll try to call Apple tomorrow when their first string help desk is available. But I don't expect to get any more success than everyone else has had.

In MacOS 15.1 is more broken in Time Machine for use with NAS

When removing and adding back the NAS to the Time Machine devices:

1. Time Machine shows you all folders even though they are not designated Time Machine folders - it shows all folders that are currently connected to the Mac, whether or not marked as Time Machine folder.
2. the dialogue, where one is supposed to enter the logon data of the credentials of the NAS cannot be edited. It is prefilled with the user of the MacOS, but you can enter only one letter from the password. At least you can add credentials that you have saved in passwords, but if you haven´t saved it in passwords, you cannot enter anything.

Currently only backups to external hard drive continue to work.

Error message: "The network disk disconnected from your Mac while backing up"

• With Synology NAS is no backup is possible,
• backup old Time Machine settings fails (running in the same setup since 2018),
• switching off firewall no longer works.

I found a solution for me and Time Machine backups are now working. I had to remove my Time Machine target in the System Settings and had to reset the broadcast setting on the NAS:

After that Time Machine found the Time Machine target again and I could re-attach to the backup and continue. Now Time Machine works again.

Thanks, turning off firewall finally got time machine to work again. Hopefully they fix this.