HW RAID does not read every sector blindly, there is a level of error detection there. And an errored sector in one read does not mean it errors in every read.
Now, the error detection schemes at the disk level may be insufficient. I don't know enough about how it's done on modern drives (but I suspect that every manufacturer has its own scheme).
Now, the error detection schemes at the disk level may be insufficient. I don't know enough about how it's done on modern drives (but I suspect that every manufacturer has its own scheme).