In case you missed the news, beta-testers of Big Sur have revealed that macOS 11.0 can save its backups to APFS volumes, indeed those are now the preferred format for backup stores for both local and network Time Machine backups. Although Apple doesn’t yet include this in the list of Big Sur’s features for users, indications are that this is intended to be a feature of the first full release later this year.
What happens during a backup to APFS is quite different from the normal process in Catalina, and when the backup is complete, the Finder creates a snapshot and uses that to give the illusion that the backup is just another folder containing everything which you expected to be backed up. Quite how it arrives at this is more of a mystery: in some cases, Time Machine backs up just the parts of a file which have changed, which can lead to economy of space used by that backup.
My free utility The Time Machine Mechanic, known for short as T2M2, works by analysing the entries made by Time Machine in the log. Normally when a new major release of macOS is in beta-testing, I avoid trying to make changes to T2M2 until the final release, as keeping pace with all the changes in each beta can waste a lot of time. With Big Sur, things are different, as its changes are so substantial.
T2M2 version 1.15 therefore adds a new button which generates a summary of previous backups in terms of their main events, such as mounting and unmounting snapshots. It also reports in detail the breakdown of items to be backed up (“events” collected from the FSEvents database), and, when the backup is complete, an analysis of different methods of backing up. The latter is important as it reveals how many files have been “delta copied”, which I understand to mean that they were backed up as a changed block instead of the whole file.
As the log messages written by Time Machine stabilise during the beta phase, I will refine and improve that information so that it provides the meaningful functional summaries already seen in the main backup analysis, which also holds good for Big Sur systems.
If you’re testing the Big Sur betas, I’d strongly recommend that you test out Time Machine backups, particularly those to APFS volumes, which are now the default. Time Machine is normally one of the least tested parts of macOS before it’s released, and needs all the testing it can get. If you do encounter problems, please report them to Apple so that those bugs can be fixed before Big Sur is released.
Hopefully this new version of T2M2 will help you do that, and gain insights into the new mechanism for backing up. Additional detail is also available from the Time Machine log feature in Mints, and of course in Ulbow and Consolation.
This new version of T2M2 also improves documentation, and is a Universal App so it should run natively on both Intel and Apple Silicon Macs. Version 1.15 is now available from here: t2m2115
from Downloads above, from its Product Page, and through its auto-update mechanism.
If you’re running an Intel Mac and have any problems, please let me know. I’ll leave the last Intel-only release available on its Product Page in case you’d prefer to revert to that.