Abstract: NoSQL data management systems have been widely used in Web data management and processing applications, for their high scalabilities and fault tolerence. The fault tolerence is achieved by using new consistency models and data replications in clustered systems. In this paper, the mechanism and implementation details of five representative NoSQL systems, i.e. Bigtable, HBase, Dynamo, Cassandra, and PNUSTS, were discussed and analyzed, after a general introduction to the principles of consistency preserving and fault tolerent processing. Furthermore, the impact of these technologies on system availability, performance and workload balance, was analyzed. Finally, their influence on the design of inmemory database management systems was discussed.