| Various ways. Drives sometimes are worse at their internal error detection than you might hope, and might return incorrect bytes. You might have faulty hardware flipping bits between when you computed a checksum/parity/etc over your data and when you wrote it out, either in memory, or over the wire. You might have a software bug or an interaction with a hardware erratum that causes the CPU to misbehave and mangle your bits in certain cases, maybe around switching from running code in a VM to not and back. You might have had, say, the Samsung HD204UI hard drive, which loses data after it tells the OS that it's written because of a bug around its write cache, so you get no error back, but you go to read the data back later and it's actually whatever was there before you tried overwriting it. SSDs, NVMe and otherwise, _can_ fail in ways that aren't just vanishing from the bus, it's just much less common than with mechanical drives, IME. I have sometimes seen SSDs return incorrect bytes inconsistently or consistently, or start spitting up read/write errors rather than entirely vanishing from the bus. Each of the above examples is a real thing I saw happen. None of them is particularly likely, plenty of people never have dumb shit like any of that come up. But it's not never. |