Deleting a snapshot removes the snapshot from the Snapshot Manager. The snapshot files are consolidated and written to the parent snapshot disk and merge with the virtual machine base disk.
Deleting a snapshot does not change the virtual machine or other snapshots. Deleting a snapshot consolidates the changes between snapshots and previous disk states and writes all the data from the delta disk that contains the information about the deleted snapshot to the parent disk. When you delete the base parent snapshot, all changes merge with the base virtual machine disk.
To delete a snapshot, a lot of information needs to be read and written to a disk. This can reduce virtual machine performance until consolidation is complete. Consolidating snapshots removes redundant disks, which improves virtual machine performance and saves storage space. The time it takes to delete snapshots and consolidate the snapshot files depends on the amount of data that the guest operating system writes to the virtual disks after you take the last snapshot. The required time is proportional to the amount of data the virtual machine is writing during consolidation if the virtual machine is powered on.
Failure of disk consolidation can reduce the performance of virtual machines. You can check whether any virtual machines require separate consolidation operations by viewing a list. For information about locating and viewing the consolidation state of multiple virtual machines and running a separate consolidation operation, see vSphere Virtual Machine Administration.
Use the Delete option to remove a single parent or child snapshot from the snapshot tree. Delete writes disk changes that occur between the state of the snapshot and the previous disk state to the parent snapshot.
You can also use the Delete option to remove a corrupt snapshot and its files from an abandoned branch of the snapshot tree without merging them with the parent snapshot.
Use the Delete All option to delete all snapshots from the Snapshot Manager. Delete all consolidates and writes the changes that occur between snapshots and the previous delta disk states to the base parent disk and merges them with the base virtual machine disk.
To prevent snapshot files from merging with the parent snapshot if, for example, an update or installation fails, first use the Restore command to restore to a previous snapshot. This action invalidates the snapshot delta disks and deletes the memory file. You can then use the Delete option to remove the snapshot and any associated files.