Understanding Space Reporting: To understand this behavior, you have to look at how Purity calculates capacity. Pure Storage uses a data reduction engine where data is deduplicated and compressed.
Volume Space vs. Shared Space:
Volume Space: This represents the unique data belonging to a specific volume that is not shared with any other volume via deduplication or snapshots.
Shared Space: This represents the data that is common across multiple volumes or snapshots. If you have two volumes that are clones of each other, most of that data is "Shared." The "Shift" Mechanism: When a volume is deleted (and potentially eradicated), the data it once shared with other volumes no longer needs to be "shared." Imagine Volume A and Volume B share 100GB of data. That 100GB is accounted for in Shared Space.
If you delete Volume B, that 100GB of data is now only referenced by Volume A.
Consequently, that 100GB is moved from the Shared Space bucket into Volume A's Volume Space bucket.
Net Result: The total physical space used on the array remains the same initially, but the accounting shifts. You see a decrease in Shared Space and an identical increase in the Volume Space of the remaining volumes that held those deduplication references.