It's much more about desired usage patterns than amount of storage. Cassandra and RDBMS's differ quite a lot in how you replicate, consistency guarantees, perf

It's much more about desired usage patterns than amount of storage. Cassandra and RDBMS's differ quite a lot in how you replicate, consistency guarantees, performant read patterns, performant write patterns, how you handle recovery, etc... If you intend to bring anything to scale it helps to understand the strengths and weaknesses of the underlying architecture.