Hi Tomasz,
naively judging from your vocabulary it seems that you know quite a bit more about this than I do (heh, I've already said that once in this thread), but I've spotted one thing you definitely forgot, so there may be others hidden within the thicket of your technical terms:
Tomasz Wegrzanowski wrote:
- filesystem resides in kernel and uses extremely very fast context switches between kernelspace and userspace, database server has to communicate using sockets, what's MUCH slower.
What you're forgetting here is that even if you use file systems, you will still have to use sockets to transfer the data to the webserver, except in the special case where they happen to be on the same machine. Relying on this special case is a serious sacrifice of architectural flexibility. I do not expect the webserver and the database to remain on the same machine for very much longer.
Greetings, Timwi