Q:

Cassandra data persistence with and without flushing the node

Does Cassandra not persist the tables to disk if I don't do nodetool flush
I created the table and keyspace using CQL but I only saw the *-data.db file when I did a flush.
Without it, the data will be lost?

A:

When data is written to a node it is first written to the commitlog on disk, and then it is written to a memtable in RAM. 
Cassandra will flush the memtable from RAM and write it to an SSTable on disk when its data footprint exceeds the memtable_cleanup_threshold. Only when this happens will the commitlog be cleared. Nodetool flush converts all memtables to SSTables, even if the memtable_cleanup_threshold is not met.
So the answer is no, your data will not be lost. Eventually the memtable size will meet the threshold, and be written to an SSTable on the disk. 

