Ada-WL: An Adaptive Wear-Leveling Aware Data Migration Approach for Flexible SSD Array Scaling in Clusters

Recently, the flash-based Solid State Drive (SSD) array has been widely implemented in real-world large-scale clusters. With the increasing number of users in upper-tier applications and the burst of Input/Output requests in this data explosive era, data centers need to continuously scale up to meet real-time data storage needs. However, the classical disk array scaling methods are designed based on HDDs, ignoring the wear leveling and garbage collection characteristics of SSD. This leads to penalties due to the vast lifetime gap between extended SSDs and the original in-use SSDs while scaling the SSD array, including extra triggered wear leveling I/O, latency in average response time, etc. To address these problems, we propose an Adaptive Wear-Leveling aware data migration approach for flexible SSD array scaling in clusters. It manages the interdisk wear leveling based on Model Reference Adaptive Control, which includes an SSD behavior emulator, Kalman filter estimator, and adaptive law. To demonstrate the effectiveness of this approach, we conducted several simulations and implementations on actual hardware. The evaluation results show that Ada-WL has the self-adaptability to optimize the wear leveling management parameters for various states of SSD arrays, diverse workloads, and scaling performed multiple times, significantly improving performance for SSD array scaling.