Why can quorum change when adding new nodes to Cassandra?
<p>I doubled the size of our cluster from 3 nodes to 6 nodes. We have RF=3. Also this is Datastax Enterprise 4.8.0 <code>cqlsh 5.0.1 | Cassandra 2.1.9.791 | DSE 4.8.0 | CQL spec 3.2.0 | Native protocol v3</code></p>

<p>I'm rebalancing the cluster and now we're seeing some weird errors from our application:</p>

<p><code>ERROR: core.RequestProcessor.logRequest()    Could not log request 4d96f06a-b465-4608-904f-2014a271d507 for brand 5954: com.datastax.driver.core.exceptions.WriteTimeoutException: Cassandra timeout during write query at consistency QUORUM (3 replica were required but only 2 acknowledged the write)</code></p>

<p>How can 3 replica be required when RF=3? Shouldn't quorum be 2? Also, disk usage has really ballooned on the nodes. Is this expected?</p>