virtualization

Then I think you have not looked well enough into it. As was mentioned earlier, rsync of the database files in combination with the wal logs gives you a simple backup that is immideately usable. At my earlier job, we were heavy users of postgres and used that as our main backup system. (It also makes setting up replication a snap)
So, no raw partitions, please - unless rsync and other file management tools get patched to read them... :-P

On the other hand, for any database of a certain size and importance, you probably want to have a separate partition for the database files so I could be possible to advice using a certain file system with some certain parameters to get optimal performance.