On attempting to pair a server by using a hypervisor connection with your Datto backup appliance, or when attempting to perform a backup of a system protected with the agentless backup solution, your Datto device encounters VMDK file not found errors.
- Agentless backups
These failures apply to agentless backups, and can be caused by ESXi failing to resolve a VM's address by hostname. Finding the VM is the first step of the backup process. The vddk-fuse process then mounts the snapshot from the VMWare environment for network transfer to the Datto device.
This error can also be caused by independent disks being attached to the VM. Independent disks are not affected by VMware snapshots, so the VMDK 'file not found' error can occur during pairing.
The error will have language similar to the following:
Backup Error at 10:31am Tuesday August 9th Critical backup failure: VMDK file not found: /home/agents/vm-32-SuperreliableDC/vddk-fuse/SuperreliableDC.vmdk. Check if VM mount succeeded.
To resolve this error, make sure that there is an internal DNS entry on the Configure → Networking tab of the web UI, as shown in Figure 1.
Figure 1: Configure → Networking
Make sure internal DNS entries are listed above the public entries, as shown in Figure 2:
Figure 2: Datto appliance with Server 1 and Server 2 set to internal DNS, and Server 3 set to public DNS
If you are still unable to pair the protected agent or resume backups, add the Datto device to your domain via the Configure → Networking tab of the GUI. Then, test communication to the target VM again. This step only allows you to confirm that internal DNS troubleshooting is necessary; you should not leave the device on the domain after troubleshooting.