R&D: RAIZN, Redundant Array of Independent Zoned Namespaces

ACM Digital Library has published, in ASPLOS 2023: Proceedings of the 28th ACM International Conference on Architectural Support for Programming Languages and Operating Systems, an article written by Thomas Kim, Jekyeom Jeon, Nikhil Arora, Huaicheng Li, Carnegie Mellon University, USA, Michael Kaminsky, David G. Andersen, Enriched Ag, USA / Carnegie Mellon University, USA,Gregory R. Ganger, George Amvrosiadis, Carnegie Mellon University, USA, and Matias Bjørling, Western Digital, Denmark.

Abstract: “Zoned Namespace (ZNS) SSDs are the latest evolution of host-managed flash storage, enabling improved performance at a lower cost-per-byte than traditional block interface (conventional) SSDs. To date, there is no support for arranging these new devices in arrays that offer increased throughput and reliability (RAID). We identify key challenges in designing redundant ZNS SSD arrays, such as managing metadata updates and persisting partial stripe writes in the absence of overwrite support from the device. We present RAIZN, a logical volume manager that exposes a ZNS interface and stripes data and parity across ZNS SSDs. RAIZN provides more stable throughput and lower tail latencies than an mdraid array of conventional SSDs based on the same hardware platform. RAIZN achieves superior performance because device-level garbage collection slows down conventional SSDs. We confirm that the benefits of RAIZN translate to higher layers by adapting the F2FS file system, RocksDB key-value store, and MySQL database to work with ZNS and leverage its benefits by closely controlling garbage collection. Compared to arrays of conventional SSDs experiencing on-device garbage collection, RAIZN leverages the ZNS interface to maintain consistent performance with up to 14× higher throughput and lower tail latency.“