Today organizations and business enterprises of all sizes need to deal with unprecedented amounts of digital information, creating challenging demands for mass storage and on-demand storage services. The current trend of clustered scale-out storage systems use symmetric active replication based clustering middleware to provide continuous availability and high throughput. Such architectures provide significant gains in terms of cost, scalability and performance of mass storage and storage services. However, a fundamental limitation of such an architecture is its vulnerability to application-induced massive dependent failures of the clustering middleware. In this paper, we propose hierarchical middleware architectures that improve availability and reliability in scale-out storage systems while continuing to deliver the cost and performance advantages and a single system image (SSI). Hierarchical middleware architectures organize critical cluster management services into an overlay network that provides application fault isolation and eliminates symmetric clustering middleware as a single-point-of-failure. We present an in-depth evaluation of hierarchical middlewares based on an industry-strength storage system. Our results show that hierarchical architectures can significantly improve availability and reliability of scale-out storage clusters.