GAP: A Global Wear-Aware Block Pool for Enhancing Lifetime of ZNS SSDs

The Zoned Namespace (ZNS) interface shifts the responsibility of data management to the host. However, host software tends to ignore or even fails to guarantee the wear-leveling of zones due to a lack of semantics. In this paper, we propose GAP, a device-level dynamic zone construction policy to ensure wear-leveling and enhance the lifetime of ZNS SSDs. The key idea of GAP is to break up all flash blocks within a ZNS SSD device to form a block pool. Once a zone's wear degree reaches a threshold, GAP selects the right number of flash blocks from the block pool to reconstruct the zone for the wear-leveling purpose. Experimental results based on the NVMe ZNS SSD emulator (FEMU) show that GAP outperforms the existing policy by 14.4x over ZenFS and RocksDB.