Now it's getting weird. So you are saying that the kernel might have
an extra internal buffer, which is not counted as buffer cache for
raw devices (this sounds like a terminology issue: any internal buffer
of the kernel for writing could be considered a 'cache').
Anyway, so raw devices do *not* guarantee IO finalization, which means
that in case of a crash, data written to a raw device might get lost?
This does not sound like a very usefull device...
Thanks,
Martin