Java Embedded Database for Global File System?

Normally if N clients want to read/write the same files they all connect to a file server which manages the disk reads/writes. In the same fashion if N clients want to access data in a database they all connect to the same database server which in turn manages the disk read/writes. In GFS (Global File System NOT Google File System) the clients concurrently modify the same data and manage the disk reads/writes themselves. Is there a database which allows multiple database servers to operate on the same on-disk data (which may, for instance, reside on a GFS file system)? Then, is there one which can be embedded into a Java application without the need to run a separate database server (just as Derby can be embedded)? Thanks.