FORTASA BLOG

As previously described, Flash memory inherently has limited endurance (number of program and erase cycles) before it starts to fail and information is no longer reliably retained. The intrinsic component endurance is specifically stated in the respective component data sheet. Typically, the inherent endurance is 3000 cycles for MLC NAND Flash and 60,000 cycles for SLC NAND Flash. In managed Flash storage devices such as SSDs or Flash cards, the expected life of the device is further reduced due to a Write Amplification phenomenon. To reverse this rapid degradation a Dynamic Weal Leveling algorithm was introduced.

At initialization, the Flash controller allocates all the formatted (unused) memory blocks into a unused block pool and sets up the usage counter for each block. With Dynamic Wear Leveling, every time a host would write new data to the storage module, Flash controller would select the block with least amount of usage and write the new data to it. Every time a host would erase a file, the Flash controller would free up (format) a block and place it in the unused block pool ranked by the amount of usage this block had gone through. This way with every new write or erase sequence the block usage would adjust and spread the memory wear from highest used block to the lowest use block. While this algorithm is highly beneficial to the dynamic (updated and erased) data, it doesn't improve the Flash wear for drive usage with large static partition, as with OS system files which are written once and don't typically get moved or updated, A complementary algorithm to spread the usage of the Flash blocks that store static data is called Static Data Wear Leveling.

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