If you have the time, try backup using previous version of vdr, if you dont experience the same problem...could be bug in latest vdr ver...its buggy since the 1st day it is borned anyway
If you dont have problem with older ver, i suggest to log a call to vmware tech
Or try NFS from another host just for the sake of testing...it may sound strange...but could lead to brighter future
-vExpert 2010