MacOS – Time Machine always makes a full backup

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I have a new iMac running OSX 10.12.4. It has an internal Apple-Supplied 512Gb SSD, of which about 140 Gb is used. As with my previous machine, I use Time Machine to backup on to an external 2Tb hard disk.

However, I find that every TM backup appears to be a full backup, not an incremental backup.

How can I get Time Machine to make proper incremental backups, as it’s supposed to?

By way of background,

  • Each backup takes a very long time; so long that it cannot backup hourly because it’s still completing the last backup.
  • On the Preferences panel it tells me that it is backing up … GB of 131 GB.
  • The space left on the drive corresponds to multiplying the number of backups by the full amount of data.
  • After about 18 backups, it starts deleting old backups
  • I get the disk full message too soon

So I am convinced that they’re all full backups.

I have tried everything I can think of, including:

  • turning it off and on again
  • re-formatting the drive
  • replacing the drive
  • reinstalling the OS
  • deleting the plist, as per Pondini’s web site
  • removing some software suspected of interfering with TM
  • excluding additional folders
  • putting chicken feathers in a paper bag and waving it around my head

I have spent countless hour with Apple support. As a desperation move, they now want me to do a clean install, which, in my opinion is going too far, and certainly not something I am enthusiastic.

I am aware of this question: Time Machine keeps doing full backups

but

  • it’s 5 years old
  • the asker says that TM also does incremental backups
  • despite the accepted answer, the question is not really answered

Best Answer

Backups are managed via Apple File System Events (not Spotlight) https://en.wikipedia.org/wiki/FSEvents

It seems most likely that something is touching your files in a way that convinces TimeMachine a new copy is needed. There could also be something damaging the FSEvent cache which would cause TM to create a new backup.

You might want to check the system console log and see if there are any messages there that hint at the underlying problem.

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