[CentOS] LVM filters not working?

Hi,
I'm trying to set up a redundant DRBD system but I'm running into 
trouble when I try to define a volume group. The physical backing device 
for the drbd resource /dev/drbd0 is /dev/vdb1. The problem is that when 
I do a "pvs" on the command line the physical volume is shown as 
/dev/vdb1. So I tried the following filter in /etc/lvm/lvm.conf:

filter = [ "r|/dev/vdb.*|", "a/.*/"

But this doesn't seem to haven any effect at all. The system still sees 
the volumen group on /dev/vdb1. Also various how-to's on the net say I 
should pay attention to deleting /etc/lvm/cache/.cache which makes sense 
but this file is never created.

Any ideas what might be going on here? I'm trying all of this on CentOS 6.

Regards,
   Dennis