No, what I meant is while you are upgrading a node, if other goes down for whatever reason you are hoing to have a bad time. You will be handling the load of 3 nodes into 2, making it more probable to end up having only one. And yes, that's something that affects any type of clustering and that's why you try to avoid as much as you can expensive or long operations in the best way. But you need to be aware and ready in case it happens