Today is a day of file systems, I'm currently working on the file layer general design and there are some feature to implement, well, I can told that it's a several features implemented may.
The first is a copy-on-write feature, well it might be implemented over the file system implementation.
while you have an vnode on top of the implementation you may create a virtual remote link to other file system vnode, and it will goes transparently for implementation. When you will got a miss on the block device of the current filesystem you may take this data from another one, remotely.
Another case of this feature is a creating a new function that will clone files in the fast way, just creating a shadow vnode on the destination file system.
I will research this cases later and write it here, it's not so good to write it in bus.