@JimWen The data won’t be removed from disk when you drop/delete anything. The delete operation is logical which means a new entry with delete marker will be added and it will be eventually removed (along with the older keys) by compaction/garbage collection. In simple words, the disk usage won’t be affected instantly by the drop operation.
As for the data showing up in the /state endpoint, that shouldn’t happen. Which version of dgraph are you using? Can you share some logs? It might be possible that the state endpoint is reporting stale data.