Symmetric Active/active Metadata Service for Highly Available Cluster Storage Systems

In a typical distributed storage system, metadata is stored and managed by dedicated metadata servers. One way to improve the availability of distributed storage systems is to deploy multiple metadata servers. Past research focused on the active/standby model, where each active server has at least one redundant idle backup. However, interruption of service and loss of service state may occur during a failover depending on the used replication technique. The research in this paper targets the symmetric active/active replication model using multiple redundant service nodes running in virtual synchrony. In this model, service node failures do not cause a fail-over to a backup and there is no disruption of service or loss of service state. We use a fast delivery protocol to reduce the latency of total order broadcast. Our prototype implementation shows that high availability of metadata servers can be achieved with an acceptable performance trade-off using the active/active metadata server solution.