Where is my data?

[AJ]

Is there an official deterministic formula to compute the various 
subsets of a given cluster that comprises a complete set of data 
(redundant rows ok)?  IOW, if multiple nodes become unavailable one at a 
time, at what point can I say <100% of my data is available?

Obviously, the method would have to take into consideration the ring 
layout along with the partition type, the # of nodes, 
replication_factor, replication strat, etc..

Thanks!