Timemachine Back-up in MacOS 26 (Tahoe) does not work on Synology DS920+ NAS

It works!

The secret was to open the sparsbundle in disk utilities, where I found a longer name for the spartsbundle, where our Swedish characters were used. Exchange those characters to anything else in the span of a-z, hit return, and try two more TM-backups. The second one flies as the wind! Beautiful! Thanks all!

[Precheck]

Please kindly follow the steps below to change settings on your Mac.

1. Open Terminal on macOS, and edit /etc/nsmb.conf with vi:

• • sudo vi /etc/nsmb.conf

1. Change the value of signing_required from no to yes:

• signing_required=yes
  • 

1. Press the Esc key, then type ZZ or :wq to save the changes and exit vi.
2. Reboot your Mac.

Once you have completed the steps above on your Mac, please continue with the steps below to check settings on both your NAS and Mac.

[On your Synology NAS]

1. Ensure that DSM is properly configured for Time Machine backups. Try creating a new shared folder and set it as the Time Machine backup folder, rather than using the original one.
2. Ensure your NAS has enough free space.
3. Make sure the following options are selected in Control Panel > File Services > SMB > Advanced Settings > General:

• Maximum SMB protocol: SMB3
  • Note: Time Machine backups require SMB3, so please change it back to SMB3 if it was modified.
  • Enable Opportunistic Locking
  • Enable SMB2 Lease
  • Enable SMB Durable Handles (Cross-protocol file locking will be disabled)

1. Confirm the following options are enabled or properly set in Control Panel > File Services > Advanced> Bonjour:

• • Enable Bonjour service discovery to locate Synology NAS
  • Enable Bonjour Time Machine broadcast via SMB
  • Set Time Machine Folders

The solution proposed by karel250 worked like a charm. I had the letter "ä" on the volume. An ordinary letter in Swedish but not in English. I changed it to the letter "a". Fixed my time mashine.

Thanks you karel250.

Yes, this worked (karel250)! In czech language system set the route in the .spuresbundle to "Záloha svazku ......" I rename this to "Zaloha svazku...." and TM worked.

Apple have to fix this problem. System automaticaly create route "Backuf of......." translated by language setting with diacritic. It make a problem.

I had the same issue. "Reservekopieën <computername>" is a name given by MacOS so I guess anyone using MacOS in Dutch (and most likely Flemish) will suffer from this issue. I solved it by translating "Reservekopieën" back to "Back-ups". Note that this only concerned the name of the disk when the sparse bundle is mounted.

This means that this would fail in the Netherlands at all times as it always starts with "Reservekopieën <computername>"?

In my case it did and I had to change the entire name. Thank you @karel250 for the fix!

You could try deleting the destination in Time Machine settings, then re-adding it (select the option to claim the backups on the re-added drive).

I am experiencing the same issue. Based on the analysis so far, it appears to be a macOS 26 problem rather than an NAS issue. When the existing backup is deleted from the NAS, and a new storage is added followed by starting the backup, the network transmission increases to around 300 MB but then stops shortly afterward. At that point, folders and files are created normally on the NAS. If it had been a permissions issue, the connection would have failed from the beginning.

It seems that the problem occurs during the process of creating a Time Machine backup on macOS.

I hope this can be resolved soon.

Hello,

I have the same problem with a new clean installation of macOS Tahoe 26. I back up data not only to Synology but also to Truenas, using the SMB protocol in both cases. Backups do not work in either Synology or TrueNAS. The backup stops at the "Preparing" stage, regardless of whether encryption, username, or password is enabled. On my other laptop with macOS Sequoia 15.7, backing up using the SMB protocol works without any problems.

In my case, the issue was caused by Korean characters included in the Time Machine image. After changing the image description to use only English, the backup proceeded normally. Thank you. karel250

.

I have a Synology DS223j configured based on Synology's kbase article, and it's backing up my 16" M4 Pro MacBook Pro running macOS 26 just fine, and has been doing so since I installed Tahoe yesterday. Last backup completed a few minutes ago.

Have you tried restarting the NAS?

I have two NAS, one Synology and one QNAP, and after installing Tahoe both time machine backups stopped working. Time machine says that the backup location is unavailable after a short while. I have not touched any configuration. Deleting old backups makes no difference. Tahoe is broken

Aha, unfortunately I cannot offer any other advice, I am not an IT expert. I consulted this problem with Apple and Synology and after sending logs from the NAS I received this response from Synology. Your problem is probably somewhere else. I recommend contacting Synology – I believe you have a DS224+ as you wrote, you will have to get through AI to a live technician who will guide you on how to send logs from the NAS. Once you upload them to Synology support, within about 3 days the logs are reviewed and they will send a solution. I have had a good experience with Synology. Unfortunately, I do not have any other immediate advice… I am sorry… I am a lawyer and IT is just my user hobby xD

Also on the previous version of MacOS I had problems using my Synology for Time Machine backups. My MacBookPro M1 would loose connection to the NAS every time it came back from sleep. I fixed this installing Automounter, since then I had no problems. Until Tahoe.....

In order to have Time Machine backups with Tahoe on my Synology I had to start from scratch...

I’m experiencing the same issue – Time Machine shows the following error: “Time Machine can’t complete the backup to ‘Time Machine’. The backup disk is not available. Make sure it is connected or select a different backup disk.”

Regular connection to the NAS disk over the network works fine. However, after the update, direct access to the NAS via the Finder sidebar (where I had created a shortcut pointing directly to a specific folder on the NAS) also stopped working, even though it used to work before. Creating a completely new backup on a new disk on my Synology NAS (DS418) did not help either.