Time Machine keeps hourly backups for 24 hours by default before purging for daily backups and I'd like to extend this further (to a week of hourly backups). Is there a way to change the backup retention policy config to allow for this? There doesn't seem to be an option in the UI.

Failing this, I'll have to install something else and I'd rather stick with Time Machine because of a fairly large initial backup (millions of files, TB's of data, already under backup with Time Machine)

  • 24 hours, not 48 for hourly backups – Gilby Apr 22 '15 at 8:02
  • What's the use case - what specific type of file needs more retention? Are you aware that Time Machine flattens backups so that files that existed in an interval that is to be deleted can be moved to the daily interval? Have you tracked an actual file you need kept? – bmike Apr 24 '15 at 12:40
up vote 3 down vote accepted

The answer is this isn't easily done. Apple doesn't expose the timing which means it's likely to change if you apply any updates to the system or the change might even break backups so they don't run.

I've left a comment asking about the use case. I've employed scripts to get around this in several cases for customers, but I'd need to know more about your actual use case before providing an alternate solution that would work even with the default Time Machine scheduling.

One such script / app BASED on Time Machine is one called rsnapshot (which is legal on apple products afaik (license wise) and you CAN set timing and frequency rather easily..

There is no way for the user to change the backup retention policy of Time Machine, and I'm not aware of any third-party apps exist that extend it with that kind of configurability either.

The third-party apps that do exist can only flip Time Machine on and off for you to achieve a less frequent backup schedule than hourly. There is one on the AppStore called TimePreserver to manually back up your backups, but it cannot be run as a scheduled service.

You could potentially write a maintenance script to run periodically that would open the Time Machine server and copy off the hourly backups for safe keeping elsewhere. But then to recover that information, it's unclear to me whether it would be as simple as copying the hourly backup files back to the Time Machine server and trying to access them via the Time Machine client interface. This is something that you might test before writing the script.

You could also try preserving the hourly backups on the server-side by doing something similar with your own Linux-based Time Machine server or Time-Machine compatible NAS. You'd just have to create your own way to keep hourly backups from being deleted (an hourly maintenance script that copies them to a separate location or manages file permissions or something).

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