I have a new MacBook Air running 10.14.5 (Mojave, non-beta). The drive is 500GB and formatted APFS.
The initial Time Machine backup has been running for about 24 hours and still isn't finished.
But it has backed up more data than could ever possibly exist on the drive:
Note that it says it's backing up 683 GB (and increasing) of a 500 GB drive, when not even 200 GB of the drive has been used.
I checked the sizes of my local snapshots, and there are only 4 of them, with the following sizes:
- 502.2 MB
- 217.5 MB
- 5.4 MB
- 7.4 MB
So that doesn't come anywhere near explaining the difference.
The Time Machine drive was cleanly formatted as HFS+ right before the Time Machine backup was initiated.
So… why is it using so much space? How is it using so much space?