ZTL: A block layer ZNS driver

Solid State Disks (SSDs) utilize NAND flash for data storage. Due to the physical characteristics of NAND, host systems would require extensive modifications in order to use flash storage directly. Instead, a firmware component of the SSD, the Flash Translation Layer (FTL), enables host systems to utilize flash storage without modification. However, the FTL performs its own data placement, requiring address translation and garbage collection, leading to performance unpredictability and performance and hardware overheads, as well as an increased cost for flash storage. The Zoned Namespaces (ZNS) specification defines a novel interface for the host to interact with flash that avoids interfacing with the Flash Translation Layer and its shortcomings. In order to use the ZNS interface, a considerable amount of modification on the storage stack of the host is required, which is why F2FS is the only stable file system with ZNS support today. In this paper, we present the host-side Zoned Translation Layer (ZTL) and extend our previous work on ZTL by providing additional experiments and implementation details. ZTL provides abstractions and functionalities required by many file systems to support ZNS devices. We demonstrate the feasibility of ZTL by providing the first EXT4 implementation for ZNS devices and by comparing our implementation of ZNS support for F2FS with the native ZNS support of F2FS, showing that ZTL decreases implementation overheads for file system developers while performance is sustained or improved.