Time Machine backup to QNAP NAS fails on macOS Tahoe

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Level 1

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Time Machine backup to QNAP NAS fails on macOS Tahoe

I just purchased a new MacBook, macOS Tahoe 26.3.1, and the TimeMachine backups to my QNAP TS-264 NAS are not working. It does not go beyond "preparing to backup" when I select backup now or when it automatically attempts to backup, then generates this notice: "Backup Not Completed Time Machine couldn't back up to <my NAS IP address>". I've been backing up successfully to my NAS for a few years how using my old MacBook macOS Ventura.

My attempts to rectify this have included:

updating the NAS firmware;
applying the macOS SMB compatibility fix I read about online (nsmb.conf) (see image below);
deleted and recreated the Time Machine share folder on the QNAP NAS;
ensured the share is mounted via SMB (not AFP) and read/write privileges to the NAS backup folder are assigned; and
Ensured my MacBook's name, the NAS name, and backup destination folder on the NAS were plain english names without any special characters or spaces (ie. "MacBook2025", "HomeNAS", and "backups1")

I can successfully connect to the smb server (my NAS) in finder window and see all folders on my NAS. I can see the attempted TimeMachine backup creates ".sparsebundle" file but shortly after that it stops and generates the messages noted above. So it seems to begin but does not get too far before stopping and generating the "backup not complete" notice.

Is this a macOS Tahoe bug that needs fixed or is there something else I can try?

MacBook Pro 14″, macOS 26.3

Posted on Mar 15, 2026 2:57 PM

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Answer 1

Top-ranking reply

iamshivam

Level 2

374 points

Mar 16, 2026 3:05 AM in response to sjo62

This happens when macOS can mount the SMB share but fails during the Time Machine sparsebundle validation phase, which happens right after “Preparing to backup.” Tahoe tightened some SMB and filesystem checks compared to Ventura, so older NAS defaults can suddenly break backups even though Finder access still works. The clue is that the .sparsebundle gets created but the process stops almost immediately.

On QNAP boxes this is often caused by SMB settings that Time Machine now rejects, particularly when SMB durable handles, signing, or opportunistic locking are misconfigured. In QNAP Control Panel > Network & File Services > Win/Mac/NFS > Microsoft Networking, make sure SMB3 is enabled, SMB1 disabled, opportunistic locking enabled, and “Enable Time Machine support” is explicitly turned on for that share (don’t rely on a generic SMB folder).

Also check that the NAS volume uses ext4 and not a thin-provisioned or snapshot-heavy volume, because Tahoe sometimes aborts sparsebundle creation if the filesystem reports inconsistent block allocation. One quick diagnostic: mount the share, then run tmutil destinationinfo and log show --predicate 'subsystem == "com.apple.TimeMachine"' --last 10m right after a failed attempt — if you see SMB error 45/operation not supported, it confirms it’s the NAS SMB stack, not macOS.

In most cases updating QNAP’s SMB service package or recreating the Time Machine share with native TM support fixes it.

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Answer 2

sjo62 Author

Level 1

4 points

Mar 16, 2026 7:03 AM in response to iamshivam

@ iamshivam, thanks for that, IT IS NOW WORKING!!!

My QNAP TS-264 NAS, QTS Ver 5.2.9.3410, does not show an option to disable SMB1 but I had already set "highest SMB Version" to SMB3 and "lowest SMB Version" to SMB2. A selectable "Opportunistic Locking" was not there as a configurable option either. My storage volume type was set to "thin" and there's a drop down actions menu that allows me to convert it to "thick." I haven't done that yet, but might later. The folder I created for TimeMachine backups "backups1", under "Edit Properties" for that folder I had already enabled a setting labeled "Set this folder as the Time Machine backup folder (macOS)". Aside from the "thin" volume it appears settings were good to go but I ensured that they were.

Next steps were: I again deleted the "backups1" folder from the NAS. I also deleted it as the designated TimeMachine backups location from my MacBook TimeMachine settings and then rebooted both the NAS and the MacBook. I then re-created the "backups1" folder on the NAS, ensured appropriate folder read/write privileges for NAS user (me), and selected the "Set this folder as the Time Machine backup folder (macOS)" properties for that folder again.

I re-connected to my NAS using "Connect to Server" in MacBook finder window using "smb://HomeNAS" string and mounted the "backups1" folder and others I have. In the MacBook TimeMachine settings I added the "backups1" location again. I attempted another TimeMachine backup, assuming it would start then fail again, at which time I could run the diagnostic you mentioned above to see if the SMB error appeared.

However, one change I made in designating the TimeMachine back location on my MacBook was to set a storage limit this time. I set it at 900MB, about 3 times the size of the used portion of my MacBook 1 TB SSD. I had not tried that yet. i'n not sure if that was the problem but It worked! It is backing up now, has been for about 40 mins, and is at 104GBs and counting. All seems good!

Had it not worked, my next step would've been to convert the thin storage volume to thick.

Thanks again for the reply , much appreciated :-)

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