Architectural Techniques for Improving NAND Flash Memory Reliability
Architectural Techniques for Improving NAND Flash Memory Reliability
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发表时间：
2018-08
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通讯作者：
Yixin Luo
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作者：
Yixin Luo
原始位错误在NAND闪存中很常见，并且将来会增加。这些错误降低了闪存的可靠性并限制了闪存器件的寿命。我们的目标是通过多种低成本架构技术提高闪存的可靠性。我们表明，NAND闪存的可靠性可以提高以低成本和低性能开销，通过部署各种架构技术，知道更高层次的应用程序的行为和底层闪存设备的特性。我们通过实验表征分析闪存错误特性和工作负载行为，并设计新的闪存控制器算法，使用我们的分析中获得的见解，以提高闪存的可靠性，以低成本。我们通过这种方法研究了四个方向。(1)我们提出了一种称为WARM的新技术，通过对写热数据和写冷数据进行不同的闪存保留管理，将闪存可靠性提高了12.9倍。(2)我们提出了一个新的框架，学习每个芯片的在线闪存通道模型，并启用四个新的闪存控制器算法，以提高闪存的可靠性高达69.9%。(3)我们通过对真实的3D NAND芯片进行全面的实验表征，确定了3D NAND中的三个新错误特征，并提出了四种新技术，这些新技术可以减轻这些新错误，并将3D NAND的可靠性提高高达66.9%。(4)我们提出了一种名为HeatWatch的新技术，通过利用自愈效应来减轻3D NAND中的保留错误，将3D NAND的可靠性提高了3.85倍。
Raw bit errors are common in NAND flash memory and will increase in the future. These errors reduce flash reliability and limit the lifetime of a flash memory device. We aim to improve flash reliability with a multitude of low-cost architectural techniques. We show that NAND flash memory reliability can be improved at low cost and with low performance overhead by deploying various architectural techniques that are aware of higher-level application behavior and underlying flash device characteristics. We analyze flash error characteristics and workload behavior through experimental characterization, and design new flash controller algorithms that use the insights gained from our analysis to improve flash reliability at a low cost. We investigate four directions through this approach. (1) We propose a new technique called WARM that improves flash reliability by 12.9 times by managing flash retention differently for write-hot data and write-cold data. (2) We propose a new framework that learns an online flash channel model for each chip and enables four new flash controller algorithms to improve flash reliability by up to 69.9%. (3) We identify three new error characteristics in 3D NAND through a comprehensive experimental characterization of real 3D NAND chips, and propose four new techniques that mitigate these new errors and improve 3D NAND reliability by up to 66.9%. (4) We propose a new technique called HeatWatch that improves 3D NAND reliability by 3.85 times by utilizing self-healing effect to mitigate retention errors in 3D NAND.