Problem: The backup of some virtual machines is done using transport mode NBD instead of SAN, even if it is configured for the virtual machine or a vApp container. There might be other virtual machines on the same SAN disk, which are able to do the backup over SAN. The cause of the problem is that in previous sessions the VMware SAN lock was not released, hence new backups were not able to use the transport mode SAN and switched to NBD. If NBD mode is available only and VMware does not unlock the lock, the complete backup of the virtual machine will fail.
The message you might see in Data Protector: Virtual Machine ‘Server_a.demo.local’: Backup disk scsi0:0 using transport method NBD
Solution: When no backup of virtual machines is running check the VE-Agent host and search e.g. in c:\windows\temp\vmware-SYSTEM for folders including the machine name. Listing the content of the folder will display a lock file. It is recommended to delete the content of the complete folder. After restarting the backup of a involved machine you can see that SAN transport mode is used again. In some cases you might Need to modify the permissions for the folders to allow the removal.