Is there any database that just defines their own partition type? It always seemed strange to me that databases are so optimized, but still operate on top of the filesystem abstraction.
Quite a few databases run on raw partitions. Often the "big, old" ones. Oracle, DB2, Sybase come to mind.
To improve performance, many OSes also provided kernel extensions to provide a DB-specific alternative block-device API for faster "raw" I/O and something like "async" I/O, rather than going through the regular unix block layer. These extensions were probably only ever used by databases.
