As per sibling comment, they do most definitely work until they don’t. M3 actually started with ElasticSearch and Cassandra for index and storage respectively but then were replaced with M3DB. I mentioned the FOSDEM talk elsewhere in the thread but you might be interested in the evolution segment where it’s mentioned ”With M3DB 7x less servers from Cassandra, while increasing RF=2 to RF=3” and something that’s not on the slides but is in the talk is a reference to an order of magnitude reduction in operational overhead (incidents/oncall debugging). Both slides and video is linked from the FOSDEM talk’s page https://fosdem.org/2020/schedule/event/m3db/.