Imagine a project which requires to be able to process 50,000+ (tiny ints) writes per second. The data, once inserted, won't change. The data is a measurement on a particular time. Sub second resolution is not required (two measurements of the same device can be a second apart).

We are willing to buy/rent more hardware but not more expensive hardware (no fancy RAID etc).

The data is ordered in sets (per device), a couple of hundreds. And should thus be shown/graphed. There is no relation between devices but we do want to group them (showing, for example, 10 graphs).

The only other requirement is that the datastore is open source and *nix based and has reasonable (community) support.

What kind of datastore would you use?