Cause
When you use LUN Disk Array as UNC path from Windows 2003 machine, the free space from Windows 2003 machine is shown about parent directory instead of actual mounted LUN.
Resolution
You should share the mounted LUN, and then use that as the UNC path.
For example, your disk array is mounted on the remote machine machine1 in the C:\ drive under Folder1 as C:\Folder1\LUN. For a Windows 2003 machine, when you use the UNC path \\machine1\c$\Folder1\LUN as the mount path, the free space that is available for the C drive appears instead of the free space for the mount path. You have to share the folder LUN and use that as the UNC path. That is, \\machine1\LUN.