Symmetric Active/Active Metadata Service for High Availability Parallel File Systems

Abstract

High availability data storage systems are critical for many applications as research and business become more data-driven. Since metadata management is essential to system availability, multiple metadata services are used to improve the availability of distributed storage systems. Past research focused on the active/standby model, where each active service has at least one redundant idle backup. However, interruption of service and even some loss of service state may occur during a fail-over depending on the used replication technique. In addition, the replication overhead for multiple metadata services can be very high. The research in this paper targets the symmetric active/active replication model, which uses 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 further discuss a fast delivery protocol to reduce the latency of the needed total order broadcast. Our prototype implementation shows that metadata service high availability can be achieved with an acceptable performance trade-off using our symmetric active/active metadata service solution.