This paper surveys previous distributed storage systems and related data redundancy and fault-tolerance schemes which are introduced to overcome the impact of host churn on data reliability. Furthermore, a hybrid storage system model is proposed which offers a reliable data storage service by integrating idle storage contributed by volatile peer nodes and stable and durable storage utilities. In order to ensure high availability and durability for this hybrid storage system, we explore four reliability improvement strategies, including File Replica Strategy, File Encoding Strategy, Replica Repair Strategy, and Stable-Volatile Strategy, as well as the combination of these four strategies. Extensive simulations based on real traces are performed, in which data availability, data durability, and storage overhead are evaluated. Simulation results show that compared with previous peer-to-peer storage systems, the proposed hybrid storage system could achieve a higher availability and durability with less storage consumption, due to proposed new strategies. Finally, taking into account storage and traffic cost, the tradeoffs between storage efficiency and reliability are discussed.