With the recent performance improvements in commodity hardware, low-cost commodity server-based storage has become a practical alternative to dedicated-storage appliances. Because of the high failure rate of commodity servers, data redundancy across multiple servers is required in a server-based storage system. However, the extra storage capacity for this redundancy significantly increases the system cost. Although erasure coding (EC) is a promising method to reduce the amount of redundant data, it requires distributing and encoding data among servers. There remains a need to reduce the performance impact of these processes involving much network traffic and processing overhead. Especially, the performance impact becomes significant for random-intensive applications. In this article, we propose a new lightweight redundancy control for server-based storage. Our proposed method uses a new local filesystem-based approach that avoids distributing data by adding data redundancy to locally stored user data. Our method switches the redundancy method of user data between replication and EC according to workloads to improve capacity efficiency while achieving higher performance. Our experiments show up to 230% better online-transaction-processing performance for our method compared with CephFS, a widely used alternative system. We also confirmed that our proposed method prevents unexpected performance degradation while achieving better capacity efficiency.

The recent performance improvements in commodity hardware have made commodity server-based storage a practical alternative to dedicated-storage appliances. Because of the low reliability of commodity servers, data redundancy across multiple servers is required for high availability of a server-based storage system. However, the extra storage capacity required to enable this redundancy increases the system cost significantly. Although erasure coding (EC) is a promising approach to reducing the amount of redundant data, it is only available in systems using distributed storage. There remains the need to reduce the performance overhead of using distributed storage, which involves much network traffic and metadata processing. In this paper, we propose a lightweight redundancy-control method called "dynamic redundancy control" for server-based storage systems. Our method adds additional file metadata for EC to the local filesystem, enabling the system to take advantage of EC with reduced network traffic and metadata processing. In addition, our method dynamically controls the data redundancy in user data between replication and EC to improve the capacity efficiency while mitigating performance degradation. Our experiments show that our method achieves up to 76% less processing time for a metadata-intensive workload, up to 150% higher read performance, and up to 147% better online-transaction-processing performance than CephFS, a widely used alternative system. In addition, our method successfully improves capacity efficiency while mitigating performance degradation.