this link http://blogs.technet.com/b/josebda/archive/2008/06/24/storing-windows-server-2008-hyper-v-files-on-an-cifs-smb-file-share.aspx
Storing your Hyper-V files on a file server is pretty straightforward.
There are, however, a few of things that you need to implement this properly with Hyper-V.
First of all, remember to grant access to the computer account of the computer running Hyper-V.
This is the DOMAIN\COMPUTERNAME$ account, which you can use in the same way you would use a regular user account when granting permissions.
The second thing is that you need to do is use a UNC path when pointing to the file server.
This is a path that looks like \SERVERNAME\SHARENAME.
Using a mapped drive or mount point does not work with the Hyper-V Manager tool.
Last but not least, you need to do this at the computer running Hyper-V (or connected via Remote Desktop to that computer).
If you try to use the Hyper-V Manager tool remotely, you will get an error message saying "Failed to create external configuration store at '\SERVERNAME\SHARENAME\FOLDERNAME': General access denied error (0x80070005)".
You can work around this by using constrained delegation to allow a workstation to work on behalf of the computer running Hyper-V.
For details on that option, check http://blogs.technet.com/josebda/archive/2008/06/27/using-constrained-delegation-to-remotely-manage-a-server-running-hyper-v-that-uses-cifs-smb-file-shares.aspx.