Morning Tutorial 2: An introduction to NVMe Zoned Namespaces

Zoned Namespaces (ZNS) are bringing the first wave of Open-Channel SSD concepts to standardization in NVMe. While promising improvements in WAF, tail latencies, and cost, the fact that changes to the host software are needed is still a concern for broad adoption. In this workshop, we will cover the concepts behind ZNS and the extensions already under standardization in NVMe and then focus on the work being done in Linux to support ZNS—from the extensions to the existing zone block framework, all the way to target applications. More specifically, we will cover:

• Linux kernel ecosystem: How does ZNS fit in the Linux Zoned block ecosystem? What are the options to boot a kernel with ZNS drives and the tools to manage them?
• User-space libraries: With a number of emerging namespaces types and command sets in NVMe (e.g., ZNS, KV, Computational Storage), we need a library that allows us to abstract the details of each technology and allow for a generic programming model. Since NVMe has traditionally been block-based, such a library has never been needed. For this purpose, we are building xNVMe (Cross NVMe), which encompasses NVMe core functionality on a common API + namespace types extension (e.g., ZNS). It also allows to transparently use different transports host-device (i.e., libaio, io_uring, SPDK, other interfaces in FreeBSD). In the tutorial, we can show how to use such a library as well as how it integrates on well-known applications such as RocksDB. Note that all the work is open-source and will be upstreamed. We expect too to create and maintain packages for different distributions.
• Emulation in QEMU: QEMU supports NVMe at the moment, but the bulk of the work was de-prioritized when devices became available. However, in our OCSSD days, we learned that having emulation when the interface is not as well-known as block is very useful. For this purpose, we have implemented a full 1.3 and 1.4 support as well as ZNS support in QEMU. All the work is being upstream (as TPs are ratified). In the tutorial, we can cover how to setup QEMU to emulate ZNS devices and how to debug bugs in real hardware by reproducing them in QEMU.

Learning Objectives

• Understand the changes needed to support Zoned Namespaces in existing applications
• Become familiar with the Linux framework for Zoned devices and understand which classes of applications can benefit from ZNS
• Become familiar with the open-source support for ZNS available across the Linux stack