ZNS+: Advanced Zoned Namespace Interface for Supporting In-Storage Zone Compaction


Kyuhwa Han, Sungkyunkwan University and Samsung Electronics; Hyunho Gwak and Dongkun Shin, Sungkyunkwan University; Jooyoung Hwang, Samsung Electronics


The NVMe zoned namespace (ZNS) is emerging as a new storage interface, where the logical address space is divided into fixed-sized zones, and each zone must be written sequentially for flash-memory-friendly access. Owing to the sequential write-only zone scheme of the ZNS, the log-structured file system (LFS) is required to access ZNS solid-state drives (SSDs). Although SSDs can be simplified under the current ZNS interface, its counterpart LFS must bear segment compaction overhead. To resolve the problem, we propose a new LFS-aware ZNS interface, called ZNS+, and its implementation, where the host can offload data copy operations to the SSD to accelerate segment compaction. The ZNS+ also allows each zone to be overwritten with sparse sequential write requests, which enables the LFS to use threaded logging-based block reclamation instead of segment compaction. We also propose two file system techniques for ZNS+-aware LFS. The copyback-aware block allocation considers different copy costs at different copy paths within the SSD. The hybrid segment recycling chooses a proper block reclaiming policy between segment compaction and threaded logging based on their costs. We implemented the ZNS+ SSD at an SSD emulator and a real SSD. The file system performance of the proposed ZNS+ storage system was 1.33--2.91 times better than that of the normal ZNS-based storage system.

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@inproceedings {273709,
author = {Kyuhwa Han and Hyunho Gwak and Dongkun Shin and Jooyoung Hwang},
title = {ZNS+: Advanced Zoned Namespace Interface for Supporting In-Storage Zone Compaction},
booktitle = {15th {USENIX} Symposium on Operating Systems Design and Implementation ({OSDI} 21)},
year = {2021},
isbn = {978-1-939133-22-9},
pages = {147--162},
url = {https://www.usenix.org/conference/osdi21/presentation/han},
publisher = {{USENIX} Association},
month = jul

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