Wear Leveling in SSDs Considered Harmful: A Case for Capacity Variance

The trend of decreasing endurance of flash memory makes the overall lifetime of SSDs more sensitive to the effects of wear leveling. Under these circumstances, we observe that existing wear-leveling techniques exhibit anomalous behavior under workloads without clear access skew or under dynamic access patterns and produce high write amplification, as high as 5.4×, negating its intended benefits. We argue that wear leveling is an artifact for maintaining the fixed-capacity abstraction of a storage device, and it becomes unnecessary if the exported capacity of the SSD is to gracefully reduce. We show that this idea of capacity variance extends the lifetime of the SSD, allowing up to 2.94× more writes under real workloads.