Time Machine always makes a full backup 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
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.