Balancing Page Endurance Variation Between Layers to Extend 3D NAND Flash Memory Lifetime

Area of Science:

• Solid State Physics
• Materials Science
• Computer Engineering

Background:

• 3D NAND flash memory utilizes vertical stacking for increased capacity.
• Process variations lead to significant endurance differences between stacked layers.
• Layer endurance variation underutilizes pages and reduces overall flash memory lifetime.

Purpose of the Study:

• Investigate endurance variation characteristics across different layers in 3D NAND flash memory.
• Identify the primary layer responsible for lifetime limitations.
• Propose and evaluate a novel write strategy to address endurance variations.

Main Methods:

• Categorized stacked layers into top, middle, and bottom based on endurance.
• Developed a layer-aware write strategy (LA-Write) incorporating a write-skip unit.
• Implemented a layer-aware table to manage write-skip probabilities per layer.
• Simulated LA-Write performance using DiskSim, a popular SSD simulator.

Main Results:

• Bottom layer pages exhibit significantly weaker endurance compared to top and middle layers.
• LA-Write prioritizes write-skip operations on weaker bottom layers.
• Experimental results demonstrate a substantial increase in SSD lifetime with LA-Write.

Conclusions:

• The endurance variation between layers, particularly the weak endurance of bottom layers, is a critical factor limiting 3D NAND flash memory lifetime.
• The proposed LA-Write strategy effectively mitigates endurance variations by intelligently managing write operations.
• LA-Write offers a promising solution for enhancing the longevity and reliability of 3D NAND-based SSDs.