As best as I can tell it was intermittent read failures on some sectors, not permanent failures.

So if you keep rereading that section of the disk you eventually get all the data, save it somewhere, write a bunch of new patterns over it, then write the original data and verify it reads back correctly many times.

I believe the article's analysis about RAID is wrong though; most controllers will start resilvering or just fail a drive once it experiences too many IO errors.