Local Recovery for High Availability in Strongly Consistent Cloud Services

Emerging cloud-based network services must deliver both good performance and high availability. Achieving both of these goals requires content replication across multiple sites. Many cloud-based services either require or would benefit from the semantics and simplicity of strong consistency. However, replication techniques for strong consistency can severely limit the availability of replicated services when recovering large data objects over wide-area links. To address this problem, we present the design and implementation of ZORFU, a hierarchical system architecture for replication across data centers. The primary contribution of ZORFU is a local recovery technique that significantly increases availability of replicated strongly consistent services. Local recovery achieves this by reducing the recovery time by an order of magnitude, while imposing only a negligible latency overhead. Experimental results show that ZORFU can recover a 100 MB object in 4 ms.