Data storage has become an important issue in sensor networks as a large amount of collected data need to be archived for future information retrieval. Storage nodes are introduced in this paper to store the data collected from the sensors in their proximities. The storage nodes alleviate the heavy load of transmitting all data to a central place for archiving and reduce the communication cost induced by the network query. The objective of this paper is to address the storage node placement problem aiming to minimize the total energy cost for gathering data to the storage nodes and replying queries. We examine deterministic placement of storage nodes and present optimal algorithms based on dynamic programming. Further, we give stochastic analysis for random deployment and conduct simulation evaluation for both deterministic and random placements of storage nodes.