Nowadays, data owners tend to outsource their data to cloud storage systems to reduce maintenance costs. Because the outsourced data are no longer under control, data owners usually concern the security, availability, access performance, and storage costs of their data. Generally, data owners can deliver their concerns to service providers through establishing service level agreements (SLAs). However, existing service providers usually provide inflexible SLAs leading to the unsatisfactory services. In this paper, practical and fine-grained SLA elements are first defined to address various requirements on client concerns. Then, the short-secret-sharing (SSS) cloud storage system adopted these SLA elements is proposed to provide clients a secure and reliable storage service. Nevertheless, as the parameters, (n, k), of SSS technique have significant influence on client concerns, we further derives the influenced models between parameters and client concerns. Based on these influenced models, the SLA-aware Short-Secret-Sharing cloud storage system (S4) can obtain suitable parameters to provide clients their desired services using minimal costs. A case study is provided to present the service flow under a general scenario and demonstrates that S4 can fulfill various client requirements. Comparison result shows that the cost paid to S4 is less than that of existing cloud storage providers.