Mirroring is a popular technique for enhancing data availability. Based on this technique, this paper proposes a high-availability data objects placement algorithm with mirroring, which groups objects into redundancy sets by using RAID at the algorithm level. The redundancy allows us to reconstruct any corruption or failure of the data objects and storage nodes, thus efficiently ensuring the high availability of storage system. We quantify the availability of storage system by using Markov reward model, and the computing results indicate that the algorithm is efficient.