File System Support for Zoned Block Devices

Due to travel restrictions, Naohiro Aota could not attend the conference and their work was presented by Johannes Thumshirn, Western Digital, Inc.

Zoned block device (ZBD) support has been introduced in Linux with kernel version 4.10. ZBDs have different write constraints than regular block devices. A ZBD is divided into several zones and each zone must be written sequentially and must be reset before rewriting.

The main type of ZBD currently available is SMR HDDs. The NVMe Zoned NameSpace proposal is also being drafted to add a zone abstraction to the NVMe specifications.

Natively supporting ZBDs in a filesystem is not a trivial change. Some filesystems must rely on special block layer drivers to ensure sequential writes (e.g. ext4 and the dm-zoned device mappers). Filesystems using a copy-on-write design are better candidates for native ZBD support. Examples are F2FS and btrfs.

This talk discusses the principles of ZBD and ZNS native support in filesystems. Support in F2FS is discussed and the approach taken with btrfs is next presented. This is followed with a performance comparison between filesystems with native ZBD/ZNS support and regular ones using dm-zoned.