SSD Write Endurance 25nm Vs 34nm

[Ao1]

If I read that paper correctly it states that NAND specs are based on continual charge events, which does not leave time for charges to de-trapp. The specs are therefore worse case scenarios.

The paper points out that the P/E cycle (stress event) causes two types of problem, one relating to data retention and the other relating to endurance.

Data retention is impacted as the oxide layer weakens, which eventually results in the inability to retain data. Endurance is impacted by charges that get trapped in the oxide. If you allow time between charges there is a potential for the charges to become untrapped, which can greatly extent life. The longer the time between charges the more chance that trapped charges can dissipate.

Obviously if a SSD is writing all the time, as in the case of running the endurance app, it does not mean that all of the NAND is being charged at the same time, so even within that scenario the NAND within the SSD will have chance to recover. It can however make a significant difference.



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Link to the paper:
http://www.usenix.org/event/hotstora...pers/Mohan.pdf

The paper also mentions that the retention period of flash is 10-20 years. This is reduced as P/E cycles are incurred. For a client SSD once the MWI expires that should in theory be reduced to 1 or 2 years.

[johnw]

Data retention is impacted as the oxide layer weakens, which eventually results in the inability to retain data. Endurance is impacted by charges that get trapped in the oxide. If you allow time between charges there is a potential for the charges to become untrapped, which can greatly extent life. The longer the time between charges the more chance that trapped charges can dissipate.

Yes, data retention is primarily affected by number of erases, since each erase tends to result in oxide degradation. Write endurance may be greater if the erases are more spaced out, but the data retention is minimally affected by erase frequency.