Troubleshooting & messages · Free space and clean-up messages
Why does a local snapshot say its size isn't reported?
Short answer: macOS doesn't reliably report one snapshot's size because snapshots share data, so Storage Studio won't show a misleading number. The total for all snapshots is shown instead.
macOS reports how much space local snapshots hold together, but not reliably for each one on its own — snapshots share data with each other and with your current files. So Storage Studio says the single-snapshot size isn't reported rather than show a misleading number.
The total held by all snapshots is shown separately, and that's the figure that comes back when they're released.