[gkorland]

First it all depends on your latency requirements and TP, if you need your TimeSeries DB to support high ingest TP and low query latency a RAM based is almost the only way you can go.

Second, many Gigas is what you get from any small size server... And, on top of that Redis/TimeSeries supports an almost linear scale out which allows your memory to increase dynamically according to your needs. Last, Redis Enterprise (& Cloud) add Redis on Flash support extending your RAM to your local Flash storage.