I just wondered if there is any kind of documentation regarding some Time Machine related configuration settings, especially Interval, Delay and GracePeriod.

Interval seems to be obvious to me (least or most (?) amount of time between TM backups), but I'm not sure about the details.

Additionally, what about controlling local TM snapshots?

Thanks in advance!

  • In my experience, TM works best when left alone, but the best documentation for it is here: baligu.com/pondini/TM/Home.html
    – benwiggy
    Mar 31 '20 at 13:17
  • Thanks @benwiggy for the reference. It seems a bit outdated (2013) but the general concepts are still in use. Do you know if Apple introduced relevant changes with respect to Time Machine when the deployed APFS?
    – Sascha
    Mar 31 '20 at 21:11
  • It seems that one cannot control the generation of local snapshots with recent version of MacOS. But it was possible to disable local snapshots with sudo tmutil disablelocal at all in previous versions of MacOS. This option does no longer exist.
    – Sascha
    Mar 31 '20 at 21:41

From https://www.baligu.com/pondini/TM/13.html and based on the default values of Interval, Delay and GracePeriod one could conclude that:

  • GracePeriod (with default of 30 minutes) determines the following effect: Restarting your Mac will reset the TM schedule, but it won't run a backup immediately, even if it's more than an hour since the last one. It will wait about 30 minutes, to avoid conflicts with other things that may run automatically, or manually by the user, after startup.
  • Delay (with a default of one hour): When your Mac wakes from sleep, it will do a backup immediately, unless one was done within the previous hour. That will reset the schedule.
  • Interval (with a default of one hour): TM will start the next backup an hour after the start of the previous backup, if your Mac is awake and the backup drive is available.

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