As the below TechNet article suggests, using DFS for files is supported:
“Microsoft Lync Server 2010 communications software supports using file shares on either direct attached storage (DAS) or a storage area network (SAN), including Distributed File System (DFS), and on a redundant array of independent disks (RAID) for file stores.”
There are a few things to be aware when using DFS which may save you some time. When defining a file store in the Lync Topology Builder, the two fields required are File Server FQDN and File Share. After creating the folder in DFS and applying the relevant permissions the folder structure may look similar to below:
Thus this would be entered in topology builder as:
File Server FQDN: domain.com
File Share: rootappslync
However, topology will not accept the values you have entered.
This is a known issue in the Topology Builder and is resolved in Cumulative Update 5 (February 2012):
Therefore I advise you to install the latest cumulative update available. You should do this on all corresponding Lync servers after installing Core Components or you may receive an error while running Step 2 in the Deployment Wizard stating that the file share defined is invalid.