Storage-as-a-Service (SaaS) or Storage Service Provider (SSP) model enables users to access their data anywhere and at any time. It also can comply with a growing number of regulations. For users whose storage requirements are unpredictable and users who need low-cost storage, the SaaS model is a good choice for its convenience and efficiency. However, security and reliability of SaaS have affected its widespread use. When users store their data in the SaaS server, they mostly concern about whether the data is intact; whether it can be recovered when there is a failure.