Challenge
The Veeam Backup server or the Backup Proxy server becomes completely unresponsive when disks of a backed up virtual machine are being hot-added to the server.
Cause
If CTK parameters are enabled on the Veeam Backup server or on the Backup Proxy server, the Virtual Appliance mode cannot be used to back up machines with large disks.
Solution
Power off the Veeam Backup server or the backup proxy server and set all CTK parameters to "false" as per the following KB:
http://www.veeam.com/KB1113
If you back up or replicate Veeam components, edit properties of a corresponding job: open the Advanced Settings dialog box and disable the Use changed block tracking data (recommended) option on the vSphere tab, so that the CTK parameters are not set to "true" during the next job run.