Delayed Parity Update for Bridging the Gap between Replication and Erasure Coding in Server-based Storage.

In recent years, there has been a demand for using inexpensive general-purpose server-based storage in a wide range of applications. To use server-based storage in legacy applications such as databases and virtual desktop infrastructure where random access is dominant, it is important to enable low data access latency. Because common server-based storage uses erasure coding (EC) to reduce the capacity overhead of redundant data, the degraded write response time of EC data becomes a performance issue. The prior studies improve the write response time of server-based storage by storing frequently accessed data with replication that enables a smaller response time than EC. However, the difference in response time between replication and EC causes unstable write response time and leads to the usability degradation of target applications. We propose dynamic redundancy control with delayed parity update, which asynchronizes parity updates of EC data to achieve stable write response time for server-based storage. The proposed method redirects the write request for EC data to the replicated differential data and achieves the equivalent write response time with the replication. Our evaluations confirmed that our proposed method reduces the 99-percentile write response time to one-eighth of the conventional method and enables the stable write response time in server-based storage.