setattr for vserver over NFS

I have a number of vservers running on a Debian lenny host that I'm
planning to migrate to a squeeze host. The vservers' root filesystems
are on NFS shares from a netapp. 

I've followed the instructions to set the barrier attribute here:
http://linux-vserver.org/Secure_chroot_Barrier#Solution:_Secure_Barrier

The problem I'm having is "setattr --barrier" doesn't appear to do
anything for the NFS filesystems, as reported by showattr (it works for
other vservers on ext3 filesystems, though). I've tried this on both the
lenny and the squeeze hosts, with the filesystems mounted as both NFSv3
and NFSv4 (the netapp supports both). I've also tried mounting the
filesystems with the "noac" option, which had no effect. Here are the
package versions for the squeeze host:

linux-image-2.6.32-5-vserver-amd64          2.6.32-39                    
util-vserver                                0.30.216-pre2864-2+b1 


Does anyone have any experience with running vservers over NFS?
-- 
Dan Urist
[email protected]
303-497-2459