When I want TimeMachine to backup my computer, I usually plug my external hard drive before going to bed. Unfortunately, I am already in the position where new backups are replacing old ones on the drive. So I am quite worried when I see that TimeMachine is creating many different snapshots during the night.

Are these identical backups going to affect the oldest ones on my drive?

Or since they are identical, TimeMachine does not remove an old snapshot everytime it creates a new one?

I am a bit confused and would like to know if I need to change my backing up routine, like doing it at the same time as I am behind the computer, to be able to unplug the drive right after?


  • Which version of macos are you using and what are your energy settings in system preferences? – user151019 Apr 5 '19 at 7:26
  • I don’t use time machine for the “oh no I deleted a file I wanted to keep” rollback feature, so I just plug my external JR in every week or so and make a backup. – dwightk Apr 5 '19 at 11:27

It is completely natural for Time Machine to keep backing up when noone is using the computer.

Usually those backups will contains almost no changes, and thus they take up almost no space on the external drive because only changes are backed up. They will eventually push out old backups, but it will probably take a long while because the changes are so small.

Even when not using the computer, there are constantly made small changes to log files, etc. that are transferred over. However note that some virtualisation programs for running Windows, Linux, etc. on the Mac can cause relatively large backups to be made even when almost no user visible changes have been made inside the virtual machine.

  • I have such windows vm so now, I am worried. Also, even if the files are small, I thought that if space is not sufficient, an entire backup would be deleted, no? So even if the increase is small, it could reach the threshold when time machine deletes an entire time point? Or I am completely wrong about that? – Myoch Apr 5 '19 at 11:09
  • Is there a way to exclude the vm file from time machine? – Myoch Apr 5 '19 at 11:10
  • That's correct - when there's no more space on the external drive, it deletes an entire "time point" as you call it. It doesn't partially delete something. – jksoegaard Apr 5 '19 at 11:19
  • Yes, you can exclude files from System Preferences => Time Machine => Options... Just drag the file into the list. – jksoegaard Apr 5 '19 at 11:20

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