Abstract

Zoned Namespace (ZNS) SSD is an emerging storage solution that reduces device-level garbage collection in conventional SSDs with a block interface. It reduces write amplification significantly and provides more predictable performance. However, the sequential write constraint of ZNS SSDs poses a challenge to adopting in-storage compression, as data placement rules prevent compressed variable-length data from being packed into optimally sized chunks. When the compressed size exceeds the designated chunk size, the data must be split across multiple chunks. Such splits lead to fragmentation and performance degradation due to double reads.

In this paper, we propose Braid-ZNS, a new in-storage compression framework that leverages the Zone Random Write Area (ZRWA) to avoid read amplification when adopting data compression on ZNS SSDs. Braid-ZNS takes advantage of the Zone Random Write Area (ZRWA) by temporarily allowing in-place updates, which are normally prohibited in ZNS zones. This capability enables the system to reorganize compressed blocks within the ZRWA in a size-aware manner, preventing cases where a single logical page is split across multiple fragments. Through this reorganization, Braid-ZNS eliminates double reads by ensuring that each logical page can be retrieved with a single access. Our evaluation demonstrates Braid-ZNS can improve compression efficiency by up to 47.0% and throughput by x2.24 compared to a state-of-the-art in-storage compression on ZNS SSDs.