It's an average- presumably they don't smear files across disks byte by byte, since that would be insane. But with drives randomly breaking, at some point every

It's an average- presumably they don't smear files across disks byte by byte, since that would be insane. But with drives randomly breaking, at some point every copy of at least one file will go at once. With, say, a terabyte of files over a thousand years, you'd expect to lose a total number of files equal to 100Kb. So probably not even one, with some small chance of losing half a drive.