One way to think of it is why would you use Cassandra when you already have a filesystem? Those databases are quite raw, to be useful for a use case like monit

One way to think of it is why would you use Cassandra when you already have a filesystem? Those databases are quite raw, to be useful for a use case like monitoring you need to build on top of them to allow for ability to get data from agents, do some processing and enable efficient querying of the data.