Eliminating the Hidden Cost of Zone Management in ZNS SSDs

Abstract: Zoned Namespace (ZNS) SSDs offer a promising interface for stable throughput and low-latency storage by eliminating device-side garbage collection. They expose storage as append-only zones that give the host applications direct control over data placement. However, current ZNS implementations suffer from (a) device-level write amplification (DLWA), (b) increased wear, and (c) interference with host I/O due to zone mapping and management. We identify two primary design decisions as the main cause: (i) fixed physical zones and (ii) full-zone operations that lead to excessive physical writes. We propose SilentZNS, a new zone mapping and management approach that addresses the aforementioned limitations by on-the-fly allocating available resources to zones, while minimizing wear, maintaining parallelism, and avoiding unnecessary writes at the device-level. SilentZNS is a flexible zone allocation scheme that departs from the traditional logical-to-physical zone mapping and allows for arbitrary collections of blocks to be assigned to a zone. We add the necessary constraints to ensure wear-leveling and state-of-the-art read performance, and use only the required blocks to avoid dummy writes during zone reset. We implement SilentZNS using the state-of-the-art ConfZNS++ emulator and show that it eliminates the undue burden of dummy writes by up to 20x, leading to lower DLWA (86% less at 10% zone occupancy), less overall wear (up to 76.9%), and up to 3.7x faster workload execution.