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Context data is important information for the behaviors of the applications in a pervasive space. To effectively restore huge amount of data, tree-liked layered storage architecture are proposed, where the leaf nodes collect the data from the sensing devices located in its domain. However, the sensing devices may be moving among different domains. In order to integrate the data from the same device, related leaf nodes should upload and store the data to a certain up-layer node, called host node. This paper presents a deep study of the data storage problem and proposes an online algorithm DHS to dynamically select the host node, which reduces the communication cost significantly. We prove the correctness of the algorithm theoretically. The experiment results also show that DHS is correct and effective.