Originally Posted By: Ira L
... it takes up a lot of disk space (since your drive has to save very bit of your pre- and post-upgrade Mac). Snapshots are only retained for a day, and if you don’t have enough free space available they won’t be available at all."

It may not take up as much space as you think. Normal APFS snapshots include only the effected data sectors — not necessarily complete files. In fact you cannot restore a single file from any snapshot, you have to restore the entire volume to the state it was in prior at the time the snapshot was taken.

One other thing to be aware of in Catalina, the boot drive will have at least three separate volumes
  1. Recovery Drive <~1.06GB>
  2. Drive name <10 to 20 GB>(this is the boot system)
  3. Drive Name - Data (everything else including apps data files etc.)
As far as I know regular snapshots are only available on the Data volume so the installer snapshot would appear to be a special unique case.


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