Hello, current deployment of Cassandra for SDC is using 2.1.17 version (https://git.onap.org/sdc/sdc-docker-base/tree/base_sdc-cassandra/Dockerfile).

version 2.1.21 is available.

On Cassandra download page, it's stated that Apache Cassandra 2.1/2.2 is supported until 4.0 release which is not out but should be "soon".

And Cassandra 3.0 will be Apache Cassandra 3.0 is supported until 6 months after 4.0 

So it should be wise to see how to migrate to Cassandra 3.1

For information, AAF and Portal/Music are using Cassandra 3.1