Stop unnecessary refreshing: extending 3D NAND flash lifetime with ORBER

Due to its low cost and high performance, 3D NAND flash memory is a popular choice as the storage device in edge computing platforms. One of the critical challenges in 3D NAND flash is frequent data refresh operations to eliminate transient errors such as retention errors. The default raw bit error rate (DRBER) is usually used as a reference to decide when to apply refresh. This method is often over-conservative, resulting in excessive unnecessary refresh operations in 3D NAND flash, especially at the late-life stage. Enduring extra wearing from refresh operations, flash blocks will need more frequent refresh operations to deal with the exponentially increasing errors. To avoid the snowball effect on flash wearing, this paper proposes to minimize the number of refresh operations by exploiting the optimal RBER (ORBER). We first develop an ORBER model by conducting evaluations and analyses on a set of real 3D NAND flash chips. Based on this model, a new refresh scheme is proposed to extend the lifetime of 3D flash memory. Experiments show that, within the lifetime of 3D NAND flash memory, the proposed method can averagely reduce 75% of the P/E cycles consumed by refresh operations and improve lifetime by 2.5X with marginal overhead, compared to the traditional refresh scheme.