PADS: A Policy Architecture for Distributed Storage Systems (Extended)

This paper presents PADS, a policy architecture for build-ing distributed storage systems. A policy architecture has two aspects. First, a common set of mechanisms that al-low new systems to be implemented simply by defining new policies. Second, a structure for how policies, them-selves, should be specified. In the case of distributed storage systems, PADS defines a data plane that pro-vides a fixed set of mechanisms for storing and trans-mitting data and maintaining consistency information. PADS requires a designer to define a control plane pol-icy that specifies the system-specific policy for orches-trating flows of data among nodes. PADS then divides control plane policy into two parts: routing policy and blocking policy. The PADS prototype defines a concise interface between the data and control planes, it provides a declarative language for specifying routing policy, and it defines a simple interface for specifying blocking pol-icy. We find that PADS greatly reduces the effort to de-sign, implement, and modify distributed storage systems. In particular, by using PADS we were able to quickly construct a dozen significant distributed storage systems spanning a large portion of the design space using just a few dozen policy rules to define each system