OpenNebula

The rollback action for creating disk snapshots is to delete the existing (base) snapshot rather than the snapshot that was failed to be created.

src/vmm/VirtualMachineManager.cc:

2156     rc = tm->snapshot_transfer_command( vm, "SNAP_CREATE", os);
2157 
2158     snap_cmd = os.str();
2159 
2160     os.str("");
2161 
2162     rc += tm->snapshot_transfer_command( vm, "SNAP_DELETE", os);
2163 
2164     snap_cmd_rollback = os.str();

The snapshot_transfer_command() (in src/tm/TransferManager.cc) function inserts the snap_id value and eventually passes that on to the transfer manager.

However, since the snap_id value is computed before any action is taken, it's the same snap_id as passed to "SNAP_CREATE".

The result is if you try to create a snapshot of disk 0's snapshot 0 and it fails then disk 0 snapshot 0 is deleted, while the new snapshot (disk 0 snapshot 1, which refers to disk 0 snapshot 0) is left alone being broken all by itself

I'm really not sure how this was ever expected to work.