is it possible to use same filesystem for multiple vserver

[The MoonSeeker]

Hi,

I'd like to know if there is a system COW (used by UML) that let  
share the same filesystem between multiple virtual server, only diff  
(diffrence between the original filesystem), are saved on separate  
images. Also, I talk about snapshop or someting like that..

Is there a system that let us save memory?

Thank you