1. A method for measuring consistability of a distributed storage system, comprising: determining at least one consistency level that the distributed storage system can provide; determining a plurality of failure classes for the distributed storage system; estimating a probability of the distributed storage system to be in each of the plurality of failure classes; mapping each failure class to the at least one consistency level; and summing the probability of each failure class for each of the at least one consistency level to determine an expected portion of time that the distributed storage system provides each of the at least one consistency level, thereby providing a consistability measurement of the distributed storage system, said consistability measurement comprising a set of at least one consistency level achievable by the distributed storage system for each of the failure classes.