Let the adults speak...
As an actual, experienced, full time, production DBA, I hate the idea of depending on the database vendor for disk access code. It's a layer of obfuscation and something outside the scope of what ANY of the database vendors are actually good at. It completely breaks the Unix idea of well functioning, limited, highly specialized tools. It also ensures that the host of tools that can be employed against a regular file system are now WORTHLESS.
It's also going to be a terrible bother for the shallow end of the talent pool (which is the vast majority).
I would only deal with an RDBMS disk access layer if I absolutely had no choice.