Time Machine has undergone major changes over the last few years, both to make efficient backups from APFS, and to support backups stored on APFS volumes. It has been a couple of years since I last examined how Time Machine makes backups to APFS: this article steps through what happens when Ventura 13.2.1 makes an automatic hourly backup of an APFS volume to APFS backup storage, Time Machine to APFS, or TMA.
Scheduling
Automatic TMA backups aren’t run at fixed times, but are scheduled and dispatched by the DAS-CTS subsystems so that backups are only made when conditions are suitable. One simple rule applied is that the first backup made after a Mac starts up is delayed for five minutes, to allow other processes such as Spotlight indexing checks to be run first. DAS-CTS is explained in fuller detail in this article, using TMA as an example.
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