Mojave time machine back up failing

Since installing 10.14 have not been able to complete a full backup using time machine to external drive. All disks check out on disk utility first aid both under OS and stand alone utility under recovery. Have erased and reformatted the external drive. Still no success. Backup begins and runs up to about 80GB ok, then fails. Restart by "back up now" continues for about 500MB and then fails again. My full backup is about 900GB so I am running unprotected.

I believe this is a Mojave problem, not a drive problem.

Any ideas?

Mac mini, macOS Mojave (10.14), Samsung display

Posted on Sep 30, 2018 12:07 AM

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Posted on Feb 1, 2019 11:16 PM

After multiple failed attempts to get Time Machine to complete a full initial backup, I seem to have hit upon a workaround solution.

I noticed in Activity Monitor that two apps were always eating up a LOT of processor cycles during the failing backups - SPOTLIGHT was apparently trying to index the new backup disk as it was being written and I think NORTON SECURITY was also trying to virus-scan it at the same time.

  1. I erased the old Time Machine drive with Disk Utility and gave it a new name
  2. I shut off all Norton scans temporarily
  3. System Preferences>Spotlight>"Excluded" the new Time Machine drive from indexing and also the entire Macintosh HD (temporarily)
  4. Time Machine> unchecked "Back Up Automatically"
  5. Deleted Macintosh HD>Library>Preferences>com.apple.TimeMachine.plist and emptied the Trash
  6. Restarted the computer
  7. Quit Norton Security
  8. Double-checked to make sure everything was Excluded from Spotlight indexing
  9. Time Machine> deleted the prior Time Machine drive name and replaced it with the newly created one
  10. Time Machine> checked "Back Up Automatically" and started backup
  11. This time the full 390GB backup ran at "light speed" and completed in about two hours (via USB 3.1)
  12. Restored Norton to original settings
  13. Removed the Spotlight "Exclusion" for Macintosh HD, but retained the exclusion of the new Time Machine drive
  14. Restarted the computer and let it resume "business as usual".

PROBLEM SOLVED! You're welcome. :-)


330 replies

Feb 4, 2019 6:27 AM in response to Michael Graubart

Greetings to Michael Graubart! Today, I turned 83, and I agree with what you write completely. I started with a Commodore 64 back in 1984, I think it was. I spent liters of midnight oil studying Basic and even a bit of Machine Language, but progress has now outstripped my "learning curve". Nowadays, I simply want a computer to work for me, not the other way round. I keep saying that we are not yet in the computer age, yet — not when WE have to do all the hard thinking. Let's hope that Apple not only reads what we write here, but acts on it. "Computer, heal thyself!"

Feb 9, 2019 9:16 AM in response to speedolli

I have had a disturbing thought. Could it be that all this stuff about Time Machine not making complete backups is a red herring? I am now puzzled and confused. According to the toolbar Time Machine icon after attempting yesterday's backup (see my post two posts back from this one), my last successful backup was made on 12 January, 2019. But today I started examining what actual files, etc., were backed up yesterday (8 February), and everything I looked for that had been modified or newly created since 12 January was correctly present in yesterday's backup.


This is obviously very far from a complete inventory of what was or was not backed up. But could it be that TM is, after all, backing everything up correctly, but showing misleading information in the toolbar icon? Have any of the more technicallly-adept posters in this string any actual evidence that material has not been backed up in the recent trials with TM in Mojave?

Feb 9, 2019 10:40 AM in response to speedolli

My latest test was with a long exclusion list (see attached).

Again I erased the external 1TB disc and TM started a fresh initial backup.

But despite all that exclusions there was again TM creating way too much of backup data:

I expected about 100GB to be backed up, but TM only ended after around 800GB.

Result: I still didn't find a directory beeing responsible for this behaviour.

Feb 9, 2019 12:52 PM in response to Michael Graubart

I agree. The whole purpose of Time Machine is to be as transparent and effortless as possible. It's not the be-all, end-all for backups. It's part of a comprehensive set of tools and practices to minimize the possibility of data loss.


I've resorted to leaving automatic backups off and gingerly hitting "back up now" after I've saved and closed everything (in case I have to reboot). I do it only when I remember and only when I have time, which defeats the purpose of Time Machine's reason for existing.


Hopefully Apple has some spare cycles to fix this, now that they've fixed the FaceTime bug.

Feb 12, 2019 12:02 AM in response to Koltrasten

The most ridiculous thing after I opened my ticket, is that they told me it's normal that TM target size grows as we backup since new data is coming in.

This is totally wrong as TM is using a mechanism called Snapshot. Guess what? Snapshot... what does that mean? it means that TM makes a picture of the disk state, and backs up this content. Why does it do a Snapshot? Because, and that's its only purpose, it avoids endless loop of backing up changing/growing data.

Since I told them it's a snapshot and the explanation is bull, I don't have any followup anymore.

Instead, they should admit there is a problem, and fix it.

Everybody can make mistakes and write buggy processes, especially on complex ones like TM. Every user is ready to behave and be nice to Apple if bugs are admitted and treated.

What is not working here, besides TM, is that stubborn attitude pretending the problem is on dumb users side not knowing how to use the software, or having screwed their systems by their sole responsibility.

The problem is on TM, not on the users.

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Mojave time machine back up failing

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