NVMe SSDs provide extremely high performance and have been widely deployed in distributed object storage systems in data centers. However, we observe that there are still severe performance degradation and write amplification under the unaligned writes scenario with high-performance SSDs. In this article, we identify that the RMW sequence which is used to handle the unaligned writes incurs severe overhead in the data path. Besides, unaligned writes incur additional metadata management overhead in the block map table. To address these problems, we propose an object-based device system named NVStore to optimize the unaligned writes in cloud storage with NVMe SSDs. NVStore provides a Flexible Cache Management to reduce the RMW operations while supporting lazy page sync and ensuring data consistency. To optimize the metadata management, NVStore proposes a KV Affinity Metadata Management which co-designs the block map and key-value store to provides a flattened and decoupled metadata management. Evaluations show that NVStore provides at most 6.11× bandwidth of BlueStore in the cluster. Besides, NVStore can reduce at most 94.7 percent of the write traffic from metadata under unaligned writes compared to BlueStore and achieves smaller data write traffic which is about 50 percent of BlueStore and 65.7 percent of FileStore.

中文翻译：

---

使用高性能 SSD 在云存储中实现未对齐写入优化

NVMe SSD 具有极高的性能，已广泛部署在数据中心的分布式对象存储系统中。但是，我们观察到在使用高性能 SSD 的未对齐写入场景下，仍然存在严重的性能下降和写入放大。在本文中，我们确定用于处理未对齐写入的 RMW 序列会在数据路径中产生严重的开销。此外，未对齐的写入会在块映射表中产生额外的元数据管理开销。为了解决这些问题，我们提出了一种名为 NVStore 的基于对象的设备系统，以使用 NVMe SSD 优化云存储中的未对齐写入。NVStore 提供灵活的缓存管理以减少 RMW 操作，同时支持延迟页面同步并确保数据一致性。为了优化元数据管理，NVStore 提出了 KV Affinity Metadata Management，它联合设计了块映射和键值存储，以提供扁平化和解耦的元数据管理。评估表明，NVStore 最多提供集群中 BlueStore 带宽的 6.11 倍。此外，与BlueStore相比，NVStore在未对齐写入下最多可以减少94.7%的元数据写入流量，并实现更小的数据写入流量，约为BlueStore的50%和FileStore的65.7%。