It's even worse than that. All writes have some probability of being incorrect, even after having been written to disk properly (the programmer did the right th

It's even worse than that. All writes have some probability of being incorrect, even after having been written to disk properly (the programmer did the right thing, the OS did the right thing, the filesystem did the right thing, and the disk did the right thing). After writing, your data can be modified by actions on other cells or by simply leaving it alone completely (see read disturbance and charge leakage). Some of this can be fixed by error correcting codes, but there is still a chance of loosing data simply by doing nothing wrong. So yes, agreed++. You need to have a level of redundancy appropriate to the criticality of the data.