Agreed, I've seen reports on ElasticSearch's website that their largest customers are running petabyte-scale data on ElasticSearch clusters, but my rule of thum

Agreed, I've seen reports on ElasticSearch's website that their largest customers are running petabyte-scale data on ElasticSearch clusters, but my rule of thumb has been: HBase for petabyte-scale data, ElasticSearch and others for terabyte-scale data. As for Kafka, I was surprised to see the article lump this together with Hadoop. I've used Kafka exclusively as a messaging bus or to stream large amounts of data. It doesn't exist as a replacement to Hadoop or Big Data technologies, but as a perfect complement, because it doesn't process data, just streams / moves it efficiently.