Is there a DBMS or storage engine intended for a DBMS that does bypass the filesystem altogether? I'm not aware of any, but at the same time I don't have a full grasp of all the storage engines offered.
It almost seems like a ridiculous idea to me for a database component author to want to write there own filesystem instead of improving their DB feature set. I hear the gripes in this thread about filesystems, but they almost sound service level user issues, not deeper technical issues. What I mean by that, is the I/O strategies I've seen from the few open source storage engines i've looked at don't at all seem hindered by the filesystem abstractions that are currently offered. I don't know what a DBMS has to gain from different filesystem abstractions.