GreenCassandra: Using renewable energy in distributed structured storage systems.

We investigate how to manage an interactive service, where response time is a critical performance metric, to maximize the benefits of green energy produced from variable sources such as solar and wind. Specifically, we design, prototype, and evaluate a distributed structured storage system, GreenCassandra, which is representative of a class of important subsystems underlying many interactive cloud services. Our proposed approach predicts the production of solar energy, and then controls the number of active nodes to manage energy consumption while respecting a response time SLA. When green energy is available, GreenCassandra may activate extra servers to build up slack with respect to the SLA. When using brown energy, GreenCassandra deactivates servers to reduce energy consumption, leveraging any built-up performance slack, while observing constraints imposed by the SLA. Evaluations show that GreenCassandra can use a heuristic green-energy-aware policy to decrease brown energy consumption and cost by up to 28% and 29%, respectively, compared to a baseline energy-aware policy. Further, these savings are very close to those achievable by an optimization-based policy that has perfect knowledge of future workload and green energy production.