One aspect to consider is that Cassandra runs on a JVM. This means that you need to have at least enough random access memory (RAM) to hold the JVM heap, plus another 30-50% or so for additional OS processes and off-heap storage. Note that this recommendation is dependent on the heap size specified. Apache's recommendation of 32 GB of RAM is a good guideline for on-the-metal deployments. For cloud (production) deployments, do not go below 16 GB.