What causes TimeMachine backups to fail on NAS devices?

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'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.

Fixed in 15.1 (at least on my system) with the Firewall on. Yay!

Fixed in 15.1

Issue is fixed on 15.1, backups from TimeMachine now copy to NAS without any alterations to the settings from 14.7.

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

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.