Rejuvenator:A Static Wear Leveling Algorithm for Flash memory

NAND flash memory has the potential to become the storage alternative of the future due to its better performance and low power requirements. However reliability is still a critical issue in using NAND flash memory for large scale enterprise applications. The number of times a block can be reliably erased is limited in a NAND flash memory. A wear leveling algorithm helps to prevent the early wear out of blocks in the flash memory. It spreads the erase operations evenly across all blocks and prevents any single block from reaching its maximum erase count limit sooner than other blocks. In attempting to do so the cold data is moved to more worn out blocks thereby reducing the rate of wear in those blocks. However, the migration of cold data is an expensive operation since it induces additional erase operations in the swapping process. To overcome this problem we propose a static wear leveling algorithm, named as Rejuvenator, that maintains the variance in erase counts of the blocks within a threshold as well as reduces the cost of the additional cold data migrations. Rejuvenator uses an adaptive scheme that gradually reduces the variance in erase counts of the blocks as some of the blocks are approaching their maximum erase count limit. Our experimental results show that Rejuvenator outperforms the existing best known wear leveling algorithms.