The reliability of the large-scale cluster storage system is one important research aspect in the related domain. A high-availability data objects placement algorithm was proposed. It groups objected into redundancy sets using RAID at the algorithm level. The redundancy allowed us to reconstruct any corrupted data objects and storage nodes when it failed and assured efficiently the high availability of storage system. The availability of storage system was quantitatively analyzed by using Markov reward model, and the computing results indicate the algorithm is efficient.