Level 1

18 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

160,898 points

Posted on Jan 6, 2026 10:27 AM

When Time Machine keeps doing full backups, it’s usually because it believes each backup is going to a “new” destination. This can happen if macOS can’t reliably recognize the backup disk, the volume identity keeps changing, snapshots are corrupted, or the backup history database is damaged. Network shares can trigger this, but since it also happens on a local APFS drive, it points more toward a Time Machine state or snapshot issue on the Mac itself.

To resolve this, I’d suggest a clean reset of Time Machine’s local state and snapshots, as follows:

First, turn off Time Machine.
Then open Terminal and run tmutil listlocalsnapshots / << This will provide you with a list of all current snapshots on your Mac. You should see something like: com.apple.TimeMachine.2026-01-05-100421.local
Then remove them using tmutil deletelocalsnapshots <date>.
After that, delete the Time Machine preference file (/Library/Preferences/com.apple.TimeMachine.plist).
Reboot the Mac, re-enable Time Machine, and select the backup disk again.

Alternately, for steps 2 & 3, you can use the Disk Utility instead. From the Disk Utility select the "Data" volume. A list of APFS snapshots should appear at the bottom of the utility. If they don't, from the Utility's menubar, select View > Show APFS Snapshots. You can then select each snapshot and delete them.

If the issue persists, try disabling Spotlight indexing on the backup disk, make sure the drive isn’t being mounted under different names, and confirm the disk has at least 2–3× your data size so Time Machine can rotate snapshots properly. Finally, we can look into the Mac's system logs to see what Time Machine is (or not) doing to cause this.

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31 replies

Jan 7, 2026 7:09 AM in response to kop-95

I follow this topic cause I have the exact same behaviour / problem.

Trying to fix the issue I did your same steps many times... and now i'm trying to make first backup after reset of both the SSD drive and my qnap's HBS3 folder which for years had been my main and only solution for TimeMachine's backups.

I wonder to know if you have ever used https://tclementdev.com/timemachineeditor/ this app because it might be the issue. I've seen it's not updated since 2022... I uninstalled it but no fix unfortunately.

As you, at first I thought it was the problem of non ASCII characters and QNAP so I added as destination an SSD... nothing changed.

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

Though, I deleted all the snapshots of my Mac SSD and started backup... No changes.

I've found this topic and I'm glad for not being the only one because I was planning to Wipe all My mac, reinstall the OS and start over... now I won't do it...

Let's keep in touch in order to fix this issue!

[Edited by Moderator]

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

18 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 ** 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

18 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

18 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

18 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...

John Galt

Level 10

160,330 points

Feb 20, 2026 10:45 AM in response to iainbeanie

Most likely, whatever went wrong was related to TM expecting to back up to an APFS formatted volume.

TM will work with HFS+ but support for it is ending and those days are fading fast. Types of disks you can use with Time Machine on Mac - Apple Support explains, in Apple's typically understated manner. After decades of experience one learns to read their tea leaves.

kop-95 Author

Level 1

18 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...

Eingang

Level 1

10 points

Jan 8, 2026 2:27 PM in response to Eingang

Deleted

kop-95 Author

Level 1

18 points

Jan 8, 2026 10:36 PM in response to Eingang

Interesting, that's very close to my issue, as I have the same behaviour on my USB disk and on my NAS share.

could it be analyzed by apple ?

kop-95 Author

Level 1

18 points

Jan 9, 2026 2:47 AM in response to kop-95

Just made another test with my professional Macbook Pro, using Tahoe 26.2 too.

Backup on the same QNAP NAS, no issue, it works perfectly.

John Galt

Level 10

160,330 points

Feb 20, 2026 8:45 AM in response to iainbeanie

Turn it back on. FV is unrelated.

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Time Machine doing full backups on macOS Tahoe