ZNS: Avoiding the Block Interface Tax for Flash-based SSDs

Authors: 

Matias Bjørling, Western Digital; Abutalib Aghayev, The Pennsylvania State University; Hans Holmberg, Aravind Ramesh, and Damien Le Moal, Western Digital; Gregory R. Ganger and George Amvrosiadis, Carnegie Mellon University

Abstract: 

The Zoned Namespace (ZNS) interface represents a new division of functionality between host software and flash-based SSDs. Current flash-based SSDs maintain the decades-old block interface, which comes at substantial expense in terms of capacity over-provisioning, DRAM for page mapping tables, garbage collection overheads, and host software complexity attempting to mitigate garbage collection. ZNS offers shelter from this ever-rising block interface tax.

This paper describes the ZNS interface and explains how it affects both SSD hardware/firmware and host software. By exposing flash erase block boundaries and write-ordering rules, the ZNS interface requires the host software to address these issues while continuing to manage media reliability within the SSD. We describe how storage software can be specialized to the semantics of the ZNS interface, often resulting in significant efficiency benefits. We show the work required to enable support for ZNS SSDs, and show how modified versions of f2fs and RocksDB take advantage of a ZNS SSD to achieve higher throughput and lower tail latency as compared to running on a block-interface SSD with identical physical hardware. For example, we find that the 99.9th-percentile random-read latency for our zone-specialized RocksDB is at least 2–4× lower on a ZNS SSD compared to a blockinterface SSD, and the write throughput is 2× higher.

Open Access Media

USENIX is committed to Open Access to the research presented at our events. Papers and proceedings are freely available to everyone once the event begins. Any video, audio, and/or slides that are posted after the event are also free and open to everyone. Support USENIX and our commitment to Open Access.

BibTeX
@inproceedings {273945,
author = {Matias Bj{\o}rling and Abutalib Aghayev and Hans Holmberg and Aravind Ramesh and Damien Le Moal and Gregory R. Ganger and George Amvrosiadis},
title = {{ZNS}: Avoiding the Block Interface Tax for Flash-based SSDs},
booktitle = {2021 {USENIX} Annual Technical Conference ({USENIX} {ATC} 21)},
year = {2021},
isbn = {978-1-939133-23-6},
pages = {689--703},
url = {https://www.usenix.org/conference/atc21/presentation/bjorling},
publisher = {{USENIX} Association},
month = jul,
}

Presentation Video