Constant Time Garbage Collection in SSDs

The Flash Translation Layer (FTL) plays a crucial role for the performance and lifetime of SSDs. It has been difficult to evaluate different FTL strategies in real SSDs in the past, as the FTL has been deeply embedded into the SSD hardware. Recent host-based FTL architectures like ZNS now enable researchers to implement and evaluate new FTL strategies. In this paper, we evaluate the overhead of various garbage collection strategies using a host-side FTL, and show their performance limitations when scaling the SSD size or the number of outstanding requests. To address these limitations, we propose constant cost-benefit policy, which removes the scalability limitations of previous policies and can be efficiently deployed on host-based architectures. The experimental results show that our proposed policy significantly reduces the CPU overhead while having a comparable write amplification compared to the best previous policies.