PADS: A Policy Architecture for Building Distributed Storage Systems

This paper presents PADS, a new policy architecture that makes it easier to develop distributed storage systems. PADS is based on two key ideas. First, a distributed storage system is implemented by specifying a control plane that embodies the design policy of the system over a data plane that provides a set of common mechanisms. Second, the control plane policy is separated into routing policy which specifies how data flows through the system and blocking policy which forces reads, writes, and data propagation to wait until system consistency and durability invariants are met. The argument for PADS is simple: PADS qualitatively reduces the effort to build new systems. For example, using PADS we were able to construct a dozen significant distributed storage systems spanning a large portion of the design space.