ZNS-Cleaner: Enhancing lifespan by reducing empty erase in ZNS SSDs

Abstract

The Zoned Namespace (ZNS) interface shifts data management responsibility to upper-level applications, which reclaims space by sending the zone-reset command to ZNS SSD devices. Due to a semantic barrier between upper-level applications and ZNS SSD devices, these applications struggle to understand the state of the flash blocks within the devices and arbitrarily send zone-reset commands to the devices. This results in significant empty pages being erased (empty erase), accelerating flash block aging and shortening the lifespan of ZNS SSDs.

To solve this problem, we decouple the zone-reset command at the upper-level applications from the erase operation at the devices, and propose ZNS-Cleaner to erase the flash blocks in ZNS SSDs. ZNS-Cleaner autonomously determines the timing of erasing, rather than relying on the zone-reset command. To fully use the empty pages, ZNS-Cleaner divides the storage space into page-level strips, and adopts these strips to reconstruct a new zone at runtime. Comprehensive evaluations show that ZNS-Cleaner reduces the empty erase by 87.2%, lowers the total erase count by 51.0%, decreases the max erase count of flash blocks up to $10\times$ and prolongs the lifespan $5.2\times$ averagely in ZNS SSDs.