A Study of Invalid Programming in 3D QLC NAND Flash Memories

Abstract

3D QLC NAND flash memories are now widely applied in storage systems due to their high density. They adopt the two-step programming strategy to avoid severe program interference. This strategy results in a non-trivial time period between the two programming steps, during which the data could be invalidated from update operations. The second programming step might be performed on invalid data, which is defined as invalid programming in this work. We investigate the severity of the invalid programming issue by presenting the elapsed time between the two steps and the ratio of pages that suffer from invalid programming. By varying several parameters of the evaluated storage system, we present that the issue is common in 3D QLC-based storage systems. Finally, we introduce two pilot solutions to deal with the issue in our future work.