Comment by userbinator

While high-density NAND is definitely worrying from a data retention standpoint, your reasons don't make sense. There has been a decrease in reliability with higher densities, and unless Apple is using SLC (strong doubt) you would expect around the same as any other manufacturer.

The sibling comments mentioning endurance don't tell the complete story either; continuously writing a drive until it shows errors means the cells have become leaky enough that they can't even hold data between each write and verify pass (hours or minutes apart), and while people point to such studies as "proof" that NAND endurance isn't something to worry about, they forget that endurance and retention are inversely related, as with temperature, and this is a statistical effect, so the true specification is more like "X years/months at temperature T after Y cycles with a BER of Z"; each one of those variables can be adjusted to make the others look as good or bad as you want.