I have a customer who is backing up almost 4 TB of data through Windows Server Backup (Server 2012) onto a 12 TB external hard drive. Yes, I know there are better methods they should use for that amount of data, but I haven't talked them into that, and technically this method should work even if it isn't the best choice. So recently the backups have not been going well. If the server has just been rebooted, the backup will go ok, but will take 2 1/2 days - as a new full backup. Then when it's time for the next backup, the System event viewer will fill up with VHDmp errors (129), and either the server will completely freeze, or at least the backup will stall. And sometimes on reboot the server won't come all the way back up. although if you then hard reboot it , it will boot normally. So it' s my understanding that the VHDmp errors are related to virtual drives. But this is a physical server, not a virtual one. However, I have found that while the backup is running, if you go into disk management, it shows a virtual drive that is a replica of the drive that is being backed up. It shows up while the backup is running and goes away when it is done. So I think that is all related. But I am at a total loss how to fix this. Once a full backup is done, Windows Server Backup should just automatically do incremental backups, at least for 14 days. And I've never seen a system create a virtual replica of the volume being backed up (although I must admit I don't often go into disk management while a backup is going, so maybe it happens...). The system has just recently been reloaded on this server, so it should be pretty clean. Has anyone ever run into this? Any ideas would be appreciated! Thanks!