Preserving data commentary

I tried to rewrite the 'preserving data' section introduction, since I think InnoDB *actually* does a good job here with page checksums / crash recovery / doublewrite buffer, and is now the default.  The page checksums are validated every time a page is read from disk, so it does try hard to validate storage.

Other database systems (Oracle) have the hardware resilience features you are describing, like mirroring, but InnoDB has made an intentional choice not to offer this functionality directly.