Active Storage Mechanism for Cluster-Wide RAID System

Reliable and high-performance network I/O mechanism is a critical part of exascale storage systems. In order to improve system reliability, some storage systems use replication and erasure coding. However, this is an additional cost and requires higher bandwidth. This paper proposes a novel method to implement a zero-overhead network RAID-5 with an active storage mechanism. The proposed method focuses on the write operation of the cluster-wide (network based) RAID system, and it can be generalized to the recovery process. In general, write throughput of the storage system with erasure coding is degraded because of the additional coding computation and the increased amount of transferred data. Our proposal solves this problem and enables us to implement a zero-overhead cluster-wide RAID system by avoiding client-side computation cost and network traffic. Furthermore, our proposed method enables the system to separate the traffic of the striped data blocks (source) and the parity generation traffic. Scalability of cluster-wide RAID can be highly increased with a dedicated network for the parity generation process. In addition, we propose an efficient implementation method that utilizes an InfiniBand remote direct memory access (RDMA) mechanism to minimize the number of memory copy operations. This implementation is built with zero-copy pipelines, and enables us to use a low-overhead inter-node data processing mechanism. The measured throughput gain was 32.6% compared to that of the naive method. The results show the same performance as RAID-0, which means that our proposed method achieves the zero-overhead cluster-wide RAID.