exZNS: Extending Zoned Namespace to Support Byte-loggable Zones

Abstract

Emerging Zoned Namespace (ZNS) provides hosts with fine-grained, performance-predictable storage management. ZNS organizes the address space into zones composed of fixed-size, sequentially written, non-overwritable blocks, making it suitable for log-structured file systems. However, our experimental analysis reveals that ZNS’s write restrictions introduce notable persistence overhead. Firstly, out-of-place updates of data blocks require frequent small modifications to file metadata blocks, which are typically much smaller than a block, to record the latest logical block address. Secondly, some files, such as databases’ Write-Ahead Logging files, frequently execute synchronous small writes, with I/O sizes typically smaller than a logical block. The persistence of these file metadata and file data requires writing back the entire block even if it is only partially updated. This significantly increases the I/O latency and potentially reduces device lifespan. This paper proposes exZNS , an innovative extension of ZNS, designed to provide both regular zones and byte-loggable zones . By exposing the persistent write buffer of the opened zones on the device to the application, the byte-loggable zone allows for appending at byte granularity through a new set of APIs. To reduce the persistence overhead described above, we built exBlzFS , a novel high-performance file system for exZNS. exBlzFS selectively records the partial updates of metadata blocks to the byte-loggable zone to ensure metadata persistence, and persists file data to the byte-loggable zone at byte granularity to absorb the frequent small writes. Evaluations show that exBlzFS increases the IOPS of RocksDB by 42.7% and 76.3%, and reduces the device’s write traffic by 86% and 94%, compared with BlzFS and F2FS, respectively.