Hard drives aren't minimally redundant. The size of the magnetic regions on the platter is bounded from below by the requirement that the heads must be able to read and write them while passing over them at a very high speed.
Furthermore, hard drives are a very stable medium: they are designed to reliably retain data for years or decades without power (possibly they may retain data even for centuries if the storage conditions are right).

I think it's a bad analogy, and a cherry picked one. Contrast with how easy it is to delete data from a DRAM chip, and you'll get why analogies with modern computer hardware don't really make any sense for biological brains.