Why is my cassandra throughput not improving when I add nodes?

Question

this is a newbie question. I have tried to do my homework, but I am stuck trying to learn how cassandra will scale linearly as advertized. When I run against a single cassan

Answer 1

1) You may be maxing out the inserting client, as Chris suggested.

2) You're running VMs on a SAN, which shares IO bandwidth between all of the VMs. In effect, you're not adding capacity as much as distributing load between more virtual replicas sharing the same resources.

3) Batches aren't typically intended for speed as much combining multiple statements into single logical operations. You're putting a lot of work on your coordinator, which will eventually hurt scaling: http://docs.datastax.com/en/cql/3.1/cql/cql_using/useBatch.html