VCenter 5.1 Linked-Mode design Question

I currently have the follwoing setup for vCenter 5.1:

Windows 2008 Domain Controller ---- Windows 2008 server with vCenter/2008 SQL Server

Now I have another data center in another part of the region running its own vCenter 5.1 and join to the same domain controller above; For linked-Mode to work do i need this vCenter server use the same SQL server above or I can configure seperate SQL server for it ?

Thanks,