I've only had about a year and a half of working in that space, but can confirm that Cassandra's quite good for truly huge time-series data. If you want to record an event every time someone makes a purchase at a Wal-Mart, turn to Cassandra or a similar system.
It is also much more highly regarded as a primary data store than Elasticsearch.
It is also much more highly regarded as a primary data store than Elasticsearch.