In practice, although HDD's are meant to be able to deal with bad blocks, and remap them, I have found the opposite to be true.

(I've been working at a low level with disks for over a decade, writing data recovery apps and such)

I have found in practice that by the time a HDD develops a single bad block, 99% of the time it's on a death spiral and it's going to completely die within a month or two.

It seems like none of this bad block remapping, spare space, or anything of the sort has any effect whatsoever. The only thing that keeps them alive is being well enough engineered not to break at all.

Please correct me if my experienced misinformed me and I'm wrong.