The snapshot files are consolidated and written to the parent snapshot disk and merge with the virtual machine base disk.
Deleting a snapshot leaves the current state of the virtual machine or any other snapshot untouched. Deleting a snapshot consolidates the changes between snapshots and previous disk states and writes to the parent disk all data from the delta disk that contains the information about the deleted snapshot. When you delete the base parent snapshot, all changes merge with the base virtual machine disk.
Snapshot consolidation is useful when snapshot disks fail to compact after a Delete or Delete all operation or if the disk did not consolidate. This might happen, for example, if you delete a snapshot but its associated disk does not commit back to the base disk.
The snapshot Consolidation searches for hierarchies or delta disks to combine without violating data dependency. After consolidation, redundant disks are removed, which improves virtual machine performance and saves storage space.
When initiating a snapshot delete action, the delta disk changes are then written to the base or parent VMDK file and the snapshot is deleted. With vSphere 5, a new option called consolidate was introduced. The purpose of consolidate is if the snapshot deletion process was not successful. In the past there were incidents where a user would initiate a snapshot deletion thinking the snapshot got deleted, yet to find out later that that’s not the case. With the consolidation option, when you initiate a snapshot deletion, if the snapshot fails to delete, the VM will then generate a warning letting you know that a consolidation is required. You would then run the snapshot consolidation option and the snapshot would get committed.
The most common case for consolidation of snapshots is when your backup software fails to delete/remove the snapshot properly. As most backup software takes a snapshot of the VM and backs up the snapshot, the removeal process after sometimes fails.
wish people would stop using the "delete" for what delete "all" does. it just confuses everyone more. delete(singular) just keeps the state where it was before the snapshot. DELETE ALL consolidates and removes but writes all changes to parent, all your changes are now there.. !
> >delete(singular) just keeps the state where it was before the snapshot
Statements like this one are confusing: delete against a single snapshot merges the data into the parent. The action you describe is called "revert to snapshot"