While many people deploy Aerospike as a pure in-memory database, it also supports a hybrid memory configuration, spreading the database across RAM, SSD/Flash, and spinning disk. Here are some short and more long-answer links to address the issue. Certainly people want the best out of both worlds: more persistent data stored on cheaper disk, and faster, more ephemeral data being stored in more expensive-per-GB RAM or SSD.
https://www.aerospike.com/products/features/hybrid-memory-architecture/
http://www.aerospike.com/docs/architecture/storage.html
I'd be eager to hear feedback on folk's experience in terms of such deployments.
