ZTL: Enabling Zoned Namespace Support for File Systems

Abstract

A Flash Translation Layer (FTL) hides the intrinsic flash properties of SSDs and provides a block interface to the host. FTLs completely embedded in the firmware of SSDs must therefore duplicate host functionality, such as the translation between logical and physical blocks performed by a file system, introducing performance unpredictability and increasing device cost. Zoned Namespace (ZNS) SSDs overcome these drawbacks by only implementing limited FTL functionality inside the SSD and by exposing a more flash-friendly interface to the host. However, moving away from the block interface means that the storage stack inside the host must be modified for ZNS devices. This requires considerable effort, which is one reason why F2FS is the only Linux file system with reliable ZNS support today. This paper discusses how the Linux storage stack can be extended to simplify the process of adapting file systems to ZNS devices. It then proposes the host-side Zoned Translation Layer (ZTL), which 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.