High-density 3D NAND flash like QLC (Quad-Level Cell) is prevailing in providing large capacities for data-intensive applications. Because of the structure limitation, a two-step programming with a specific sequence is adopted in 3D QLC flash, where data could become invalid between the two programming steps. This is called invalid programming, as the second-step programming is conducted on partially-invalid wordlines (WLs). By exploiting this phenomenon, this work proposes invalid-data assisted strategies for performance and reliability boosting of valid data in 3D QLC-based flash storage systems. We first propose a high-efficiency re-programming (RP) scheme to reprogram the valid data and a high-reliability not-programming (NP) scheme to program data on the partially-invalid WLs. An adaptive data allocation (ADA) strategy for data management between the SLC and QLC regions is further introduced to reduce the occurrence of invalid programming. The simulator-based experiments show the proposed RP scheme combined with ADA can reduce the execution time for programming by 13.51%, on average. Through real-device evaluations, we present that the NP scheme can reduce the bit error rate of NP-programmed data by 32.8% of the worst page type, thus improving overall reliability, which translates to 12% reduction in refreshing overheads and 30% lifetime extension, on average. Besides, the NP scheme with ADA averagely reduces energy consumption by 4.8%.

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.