In this paper, we consider combining replication and data partitioning schemes to assure data availability, confidentiality, and timely accesses for data grid applications. Data objects are partitioned into shares and shares and dispersed. The shares may be replicated to achieve better performance and availability. We develop models for assessing confidentiality, availability, and communication cost for different placements and use the metrics to guide placement decisions. A new probabilistic security assurance model and an efficient availability computing algorithm have been developed. Due to the nature of contradicting goals, we model the placement decision problem as a multi-objective problem and use a genetic algorithm to determine Pareto optimal placement solutions.