SUMMARY
Volume Mountpoints in Windows can lead to backup failures
ISSUE
Purpose
Describe how mountpoints without drive letters can cause backup failures
Description
In Windows it is possible to define an NTFS folder as a mountpoint. These mountpoints do not have drive letters.
http://technet.microsoft.com/en-us/library/cc938934.aspx
Cause
A backup has failed. In the backup summary output, you note the inability to identify information about a volume listing the following format with a "?" where the drive letter should be, and the GUID does not match any known partitions:
\\?\Volume {GUID}\
Resolution
If the server is a physical machine, use the mountvol command for windows to remove the mountpoint. The command:
MOUNTVOL /D \\?\Volume{UUID} will remove the mountpoint for the volume listed.
If the server is a virtual server, it should be possible to use VMWare or Hyper-V backups of the machine instead of the agent backups and obtain successful backups without removing the mountpoint.
Third-Party Sources
http://technet.microsoft.com/en-us/library/cc772586(v=ws.10).aspx