Vnodes are amazing for so many reasons. The model here is pretty simple, but even still, it means you can rejuggle work without having to re-hash when adding nodes: just have the new node claim some vnodes. That's just the basics.

In Cassandra's consistent hashing & many others, you can also juggle vnodes around between nodes as you please, which, if you have hotspot vnodes, gives you some chance to add some anti- affinity for the hot vnodes.

https://docs.datastax.com/en/cassandra-oss/3.0/cassandra/arc...

Sounds like placement groups in ceph.