Several of you have asked me why a user can’t make a snapshot of their current System volume in Big Sur, immediately prior to updating it, and use that snapshot to roll back to, if the update goes wrong. This article tries to explain why that’s not as easy or simple as it sounds.
What’s a snapshot?
Snapshots are common features in modern file systems, and are one of the core advantages of APFS. The purpose of a snapshot is to record the state of the file system of an APFS volume at a moment in time. To create one, all APFS has to do is make an exact replica of that volume’s file system. That’s then stored in the same container as the volume, and any time you want, you can revert the volume’s file system to the way it was when the snapshot was made.
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