[Users] Using a layered filesystem as private dir?

[Rick van Rein]

Hello,

I've just started using OpenVZ, and it feels more natural than the
alternatives I've seen -- my compliments!

I can get a host runnig from a ZFS volume like /tank/vzdemo, which then
also gets shown at /var/lib/vz/vz-$VEID.  But what I really want to
do is use a layered FS (like aufs) as the private directory for the
container.  But trying to do that leads to an error:

bash# mount -t aufs -o br:/tank/vzdemo=rw:/tank/squeeze=ro none /mnt
bash# grep VE_ /etc/vz/conf/777.conf 
VE_PRIVATE=/mnt
bash# vzctl create 777
Private area already exists in /mnt
Creation of container private area failed

What is this trying to say?  Is there a way to do what I am trying
to do?  Did I understand well that the private area is a directory,
not a device?


Thanks,
 -Rick


P.S. To capture any "why" questions :- I am trying to share as many
     resources as possible.  Containers beat Xen/KVM/VMware in that
     respect, and when I can share the base OS and only have a thin
     layer on top, it should mean that even the buffer cache is
     shared between containers.  It also means that upgrades can be
     reduced to a minimum of repetition.