Level 1

15 points

Time Machine doing full backups on macOS Tahoe

My timemachine is not doing incremental...

I have a Macbook pro with MacOS Tahoe 26.2.

I am using Timemachine since several years, but strangely since a couple of months timemachine seems to have become crazy. It seems not to do incremental backups anymore, but full backups each time.

As an example, I have around 650 GB of data that I want to backup to a 2 TB NAS share on my QNAP NAS. Each backup tackes nearly 650 GB. With 3 backups I am done... The share becomes full and backups fail.

My understanding is that timemachine should do incremental backups and backup only new data between the two schedules, so a couple of GB per instance at max. And on another hand, when the share is full, it should clean the storage to reclaim space.

I am not sure that this is related to SMB or the QNAP NAS as I made the test today with a 2 TB USB drive, formatted with APFS, and the behaviour is the same... 3 backups and it's full and timemachine fails.

I tried deleting all my backups, recreated the share, deleted snapshots etc... but it's still failing.

Do you have any idea ?

Thanks for your help

MacBook Pro 14″, macOS 26.2

Posted on Jan 6, 2026 9:24 AM

Top-ranking reply

Tesserax

Level 10

158,166 points

Posted on Jan 7, 2026 1:27 PM

From a quick review of the log, this doesn’t look like “Time Machine choosing to do full backups” so much as “Time Machine can’t reliably *see or update* the existing backup set on the network target, so it behaves like it has to start over (or never completes enough state to remain incremental).”

The biggest red flags are the Permission denied / Operation not permitted when reading volume capabilities for the mounted Time Machine share, plus “Resource busy” when writing com.apple.TimeMachine.MachineID.plist inside the sparsebundle. If Time Machine can’t read the destination’s capabilities consistently and can’t update its identity/plist files, it can’t cleanly maintain the incremental chain.

The other repeating error, tmutil … fs_snapshot_list failed: Operation not supported, strongly suggests the Mac isn’t able to enumerate local filesystem snapshots for the source volume at that moment (or the source isn’t presented as snapshot-capable). Modern Time Machine relies heavily on APFS snapshots to produce fast incrementals. If snapshot operations aren’t available/working, backups can become much larger and “full-like,” and if the network destination is also flaky/permission-blocked, you’ll see repeated resets.

The BACKUP_IN_PROGRESS_REQUEST_DROPPED (46) is consistent with a backup getting wedged and new requests being ignored/dropped.

Ok, with all that said, the most likely causes are:

NAS / SMB share permissions or capability reporting are broken/inconsistent: (Permission denied, Operation not permitted, can’t read capabilities, can’t get remount key).
Sparsebundle is being held open/locked: (Resource busy). Often caused by NAS-side indexing/AV, another Mac trying to back up to the same bundle, stale SMB handles, or a prior mount not cleanly detached.
Source snapshot support is failing: (fs_snapshot_list … Operation not supported). These can lead to huge deltas and fragile incrementals.
Mount path / share identity instability. If the share mounts differently each time (Bonjour name changes, different subpath under /Volumes/.timemachine/...), Time Machine can treat it as a “new” destination.

Finally, here are some steps you can take to hopefully resolve this:

Confirm the destination is stable and writable:
- On the Mac: open Time Machine settings and verify it’s always pointing to the same network disk/share.
- Using the Finder, connect to the share manually, create/delete a test folder (confirms real write access).
- On the NAS: ensure the Time Machine user has full read/write on the Time Machine share and the share is explicitly configured for Time Machine over SMB.
Eliminate Resource busy / locking:
- Ensure only one Mac is using that specific sparsebundle (each Mac should have its own bundle).
- Temporarily disable NAS-side indexing/antivirus on the Time Machine share (if enabled).
- Eject the Time Machine volume, reboot the NAS (or at least restart SMB), then reboot the Mac and try again.
Check whether Time Machine is actually re-creating the backup set:
- On the Mac (Terminal):
  - tmutil listbackups (if it returns nothing / resets each run, it’s not maintaining the chain)
  - tmutil destinationinfo (confirms what destination TM thinks it’s using)
Fix the snapshot issue on the Mac:
- Confirm the source volume is APFS and not an unusual setup.
- Make sure there’s adequate free space on the Mac (snapshots can fail when space is tight).
- If third-party security software is installed, temporarily disable it and retest (some tools interfere with backupd access patterns).

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27 replies

Jan 7, 2026 7:16 AM in response to panda1988

panda1988 wrote:

IMHO all the problems started since tahoe 26.1... And it is related to the APFS filesystem and it's way to store snapshots...

It’s certainly not a generic issue with Tahoe. Time Machine continues to work as it always had for me (now on 26.2 but I upgraded to Tahoe on day one). My primary backup is to a Synology NAS, my secondary backups are to a pair of SSDs, all work normally with the usual incremental backups (and snapshots stored locally, hourly for the past day plus the most recent one to each SSD, which I connect weekly to swap one offsite).

kop-95 Author

Level 1

15 points

Jan 7, 2026 7:18 AM in response to panda1988

Ciao @Panda1988

We have strictly the same issue, the same symptoms, and made the same workarounds. I also used TMEditor in the past, but as I wiped the TM configuration deleting the TM files, it should not interfere now.

I will never format my computer for that, TM is so inconsistent in time (since more than 15 years I'm struggling with it from time to time) that he will not win ;)

Let's stay in touch, the first of us that finds a solution warns the other ! Grazie

What surprises me is that if the issue is on more than 2 macs in the world I cannot find others complaining...

Jan 7, 2026 12:07 PM in response to kop-95

I will definitely tell you my latests tests and updates! I'm doing a backup through my qnap tonight and let's see if it ends with new tahoe Beta di 26.3 (a) (25D770870b) .

The other strange thing, is not only that it doesn't do incremental backups, but also that it does not delete old ones! neither on ssd nor through nas via SMB.

I tried as well to process the log of time machine but i cannot! too many attempts and too many lines!

When you have remove TMEditor, how did you remove it?

with the uninstall button on it's own submenu or just drag n drop the app and its relatives prefs files to the trash?

I installed it with homebrew, then i noticed that i must had to uninstall it first from it's own menu, then by the terminal with "brew uninstall --cask timemachineeditor"

kop-95 Author

Level 1

15 points

Jan 7, 2026 12:56 PM in response to panda1988

yes of course it is long for each attempt...

I did not uninstall TMEditor, but I've reset the TM parameters by deleting the .plist file, and I saw that they were all reset on default values.

Yes, the logs is unreadable by a human ! But you can still use AI (I used chatGPT) to summarize and give you a first analysis.

To be honest, at the end ChatGPT gave me advises like the ones we've had here, but nothing that helped me :(

kop-95 Author

Level 1

15 points

Jan 7, 2026 1:47 PM in response to Tesserax

Thank you for this very detailed answer.

I've checked some of these :

TM is pointing to the same share, I've been able to mount it and create a folder in it with Finder
User for TM has full r/w access
There is no concurrency on the folder from multiple macs and I use one share per mac for the backups - the two other macs (my wife's and my daughter's have no issues but they use a different version, older, of macos)
no indexing/antivirus on the mac - just checked
tmutil listbackups show me one backup only (the first one, all the other consume space but do not show up) - tmutil destination info gives me the right path
source disk is APFS, and I can see a few snapshots on the disk, with few GB each - I have around 350 GB free space / 650 GB used space
But I have Bitdefender antivirus activated on the mac. Next will be to restart the whole process with the antivirus turned off maybe

As a reminder, I've made a test two days ago with an USB HDD as a destination. I've had the same bad behaviour with always huge transfers (whole capacity) where it should be incremental. That's why I am not suspecting the QNAP NAS anymore.

will do the test (but not tomorrow) with the antivirus disabled on the source mac.

Jan 7, 2026 3:02 PM in response to kop-95

I have made exact same tests and obtained same results.

and i have never had installed any AV software so bitdefender has nothing to do with that.

My Mac use a verified APFS in healthy state and i have 50% free space

kop-95 Author

Level 1

15 points

Jan 10, 2026 6:58 AM in response to Eingang

Amazing !

Thank you @Eingang !

I've just found the same post on reddit yesterday evening, but I wasn't confident enough to apply it without finding another evidence ;)

It worked perfectly, since this morning that I applied these attributes changes, Timemachine is making incremental backups.

@Panda1988, I hope you did not wipe all of your macs yet...

kop-95 Author

Level 1

15 points

Jan 6, 2026 1:31 PM in response to leroydouglas

reformat the share ? (it was a NAS share in the last example, clean as it was just bean created)

I've had the same behaviour testing a few hours ago with a brand new USB drive

Jan 7, 2026 12:49 PM in response to kop-95

My backup now is proceeding but it will take hours to end, so the troubleshooting will lasts a lot since every attempt can take 12+ hours to end on a Nas with raid 5 and 5400rpm Hard drives...