VMWare Hard Disk Query

Hello,

I have a VMWare VSphere Enterprise 4 setup at the moment all working fine.  On this platform I have a virtual machine that is a file server.  This virtual machine has two hard disks added to it, one 1.09tb and the other 1.99tb.  So if I go to edit settings on the VM and highlight Hard Disk 1 it shows me a Disk File path of: [SAN_Vol05]File/File.vmdk.  If I highlight Hard Disk 2 it shows me a Disk File path of: [SAN_Vol05]File/File_1.vmdk.  

My problem is that these have been thin provisioned on the same SAN_Vol totalling just under 3TB of required space on the SAN.  Each of the SAN_Vol's on the SAN are a max size of 2TB.  So sooner or later we will get to the stage where we will run out of space on the SAN_Vol as we have thin provisioned more space than we have available in any one SAN_Vol.  Although we have the space across multiple SAN_Vols so the hardware isnt the issue.  

I was expecting to be able to stop the File server VM, edit the disk file path and move hard disk 1 and hard disk 2 vmdk files to separate SAN_Vols each 2TB.  However to my surprise I cant see how to edit this path as it is still greyed out.

Anyone have any ideas how we can get round this issue without disturbing our live server too much?

Is there a way to amend how much has been thin provisioned as the file server has a large chunk of free space available to it still?

Thanks