ECCPM: An Efficient Internal Data Migration Scheme for Flash Memory Systems

Abstract

The copyback command can be used to accelerate data migration in solid-state drives. However, the reliability of this command is not guaranteed, posing challenges for broad utilization within the consumer electronics device. The existing algorithms for predicting the copyback threshold do not consider two issues: 1) Due to page/wordline restrictions restrictions, the accumulation of errors across pages during copyback operations is asymmetrical; and 2) The controller lacks prior knowledge about the raw bit error rate (RBER) before decoding. As a result, it is impossible to predict the frequency of copyback command execution. In this paper, we explore the mathematical models of flash programs and read operations. We further develop the state transition probability matrix for wordline-level data migration within the same plane. Therefore, we propose a predictive model for the maximum copyback threshold within the same plane. To address these two issues, we conduct tests and analyse the characteristics of error accumulation in copyback using actual chips and substitute the relative entropy of the state distribution in our prediction model for RBER. By integrating these insights, we introduce an estimated copyback count prediction model (ECCPM). The simulation results demonstrate that the ECCPM can significantly reduce latency while minimally impacting write amplification.