The endurance of NAND flash memory has been always a questionable issue for many of those who plan to buy a solid-state drive (SSD). Although it has been proven by many IT professionals that the endurance of the MLC NAND-based SSDs of today is pretty sufficient (it’s even more than enough) for any enthusiast computer user no matter how much data they use on a daily basis, many people still have a misconception about the durability of SSDs thinking they have short lifespan and will not last long enough. Back to the old days when SSDs were coming with 3Xnm MLC NAND with 5,000 P/E cycles, the concern of wearing out the SSD obsessed many people, although there was literally nothing to validate that concern. The move to ~20nm MLC NAND has reduced the available P/E cycles to 3,000, but that’s still plenty.
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Anandtech.com explained the architectural differences between SLC, MLC and TLC NAND and published a table that demonstrated the difference between these technologies, as shown below:
The main difference is that MLC stores two bits per cell, whereas TLC stores three. This results in eight voltage states instead of four (also means that one TLC cell has eight possible data values). Voltages used to program the cell are usually between 15V and 18V, so there isn’t exactly a lot room to play with when you need to fit twice as many voltage states within the same space. The problem is that when the cell gets cycled (i.e. programmed and erased), the room taken by one voltage state increases due to electron trapping and current leakage. TLC can’t tolerate as much change in the voltage states as MLC can because there is less voltage headroom and you can’t end up in a situation where two voltage states become one (the cell wouldn’t give valid values because it doesn’t know if it’s programmed as “110” or “111” for example). Hence the endurance of TLC NAND is lower; it simply cannot be programmed and erased as many times as MLC NAND and thus you can’t write as much to a TLC NAND based SSD.
Anandtech also published anther comparison table that designates the SSD life estimation for each of the three technologies as can be seen below:
This table indicates that MLC NAND SSDs can last for so long even under intensive workloads. And while most, if not all, premium SSDs are covered by 5-year limited warranty, that means you have to consume at least 140 GiB/day continuously for 5 years before the warranty expires to feel any degradation occurs in the drive performance, and that is so very huge amount of data that even the most ardent computer enthusiast cannot consume on a daily basis.
As for speed, the following table from anandtech designates how MLC surpasses TLC NAND in this regard:
This table indicates that TLC is around 50% slower than MLC NAND.