New-Tech Europe | September 2016 | Digital Edition

These red sectors above the dashed line have exceeded the maximum endurance cycles. They are now BAD sectors and can no longer be written to or read from.

Advanced leveling schemes (like Datalight FlashFX family) keep endurance cycle differences in this example between 700 and 1400, at a maximum. wear

in the flash disk to accommodate the fact that flash memory cannot simply be rewritten. The specific algorithms are beyond the scope of this paper, but the idea is to efficiently write throughout the flash before rewriting the same location. The wear-leveling scheme implemented by an effective flash manager consists of tracking the number of erases incurred on each flash erase block. In other words, both high and low use sectors are monitored. This is often referred to

as dynamic wear-leveling. As erases accumulate, the difference between the highest and lowest counts is audited. If a specific set of constraints are met, a wear-leveling operation - which swaps the least erased block with the most recently used erase block - is completed. Two parameters control wear-leveling erases; the first is a maximum difference allowed before wear- leveling erases are incurred, and the second limits the frequency of wear-

system code, will never reach the flash memory’s maximum endurance. Without wear-leveling, these low-use sectors are essentially wasted flash lifetime. Meanwhile, the disk use in Figure 2 is spread evenly throughout the disk sectors, allowing the flash disk to be reliable for its maximum lifetime. Professional Wear- leveling Implementation A properly-executed wear-leveling implementation moves data around

48 l New-Tech Magazine Europe