Testimonial (part 2):

But there was a small discrepancy involving two of those 3/4 million files. I investigated, and discovered that two of those five drives had bad sectors that were the cause of the discrepancies. Further investigation, using chkdsk, revealed that one of those five devices was so damaged that chkdsk could not even run on it. At that point, I had only four good copies out of the 12 that I thought that I had.