Is QNAP TS-133 compatible with macOS Tahoe backups?

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Is QNAP TS-133 compatible with macOS Tahoe backups?

As a preparation to getting rid of Time Capsules we at our company have set-up QNAP TS-133 devices for Time Machine backups. This was working fine under macOS 15 and earlier macOS versions.

After upgrading to macOS 26 Tahoe the Time Machine backups stopped working. Various error messages (Backup is already in use, Backup disk is not available, just after Preparing backup). This happens on all of our upgraded Macs.

The log(1) logfile shows that backupd unmounts the volume right after trying to start the backup.

Setting aside the non-working backup sparsebundles and starting new backups seems to work fine so far.

What could be the cause here? Backups were working fine before upgrading to Tahoe and stopped working immediately after upgrading. Starting a new backup from scratch seems to work as well (still testing). We can not find anything wrong with the sparsebundles of the non-working backups.

Is this a QNAP TS-133 NAS issue, a NAS settings issue or a macOS Tahoe issue or bug?

Ernst Mulder

[Re-Titled by Moderator]

Original Title: macOS Tahoe and QNAP backups

MacBook Air 15″, macOS 26.0

Posted on Sep 17, 2025 6:21 AM

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Answer 1

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Ernst Mulder Author

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Sep 18, 2025 5:05 AM in response to Ernst Mulder

Fortunately it is not the NAS but most likely a bug in macOS 26 Tahoe.

The volume name of the no longer working backup sparsebundle is "Reservekopieën van Computername".

The volume name of the newly created backup sparsebundle under Tahoe is: "Back‑ups van Computername"

This is the hint in the log(1) output that pointed me to the issue being the volume name:

backupd-helper: (TimeMachine) [com.apple.TimeMachine:MountPointValidity] Invalid mountpoint '/Volumes/Reservekopieën van Computername' - no volume mounted at this path

After changing the volume name of the no longer working backup to "Back‑ups van Computername" and re-adding it to Time Machine, the backup is operational again.

I am not certain if the localisation change from "Reservekopieën" to "Back‑ups" in Tahoe is the cause, or that Tahoe does not like the "ë" in the name of the backup volume.

Glad we have our backup histories back, and hopefully this will help others with the same issue.

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Answer 2

Ernst Mulder Author

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Sep 23, 2025 12:25 PM in response to karel250

Good to know, so in the case with Dutch localization system it is the "ë" causing the backup to fail. Still quite proud I found out myself :-)

Quite a stupid text encoding bug by the way. Does Apple actually test localized systems during development?

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Answer 3

Ernst Mulder Author

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Sep 23, 2025 12:56 PM in response to karel250

Good to know, so in the case with Dutch localization system it is the "ë" causing the backup to fail. There must be numerous languages where this goes wrong.

Still quite proud I found out the renaming solution myself :-)

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Answer 4

Sep 17, 2025 6:33 AM in response to Ernst Mulder

I suspect the issue is on the QNAP side, I use a Synology DS223j for TM backups of several Macs in the house, the one that I upgraded to Tahoe on Monday continued to back up just fine to the NAS.

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