I was making a more theoretical point that defining "durable" in terms of specific hardware isn't a very elegant definition.

In practice with VoltDB, you'll replicate to multiple machines synchronously (so you'd need to lose power to separate servers to lose data). VoltDB enterprise has command logging.

For a chat messages, I'm not sure VoltDB would be the _best_ choice, perf wise. Chat messages are usually more ephemeral - why go through the overhead of ACID for those?

For real $$$ transfers, you'll probably want synchronous WAN replication, to really ensure you never lose transactions.