Job fails with error containing “VDDK error: 1.Unknown error”.
This error is thrown by VMware VDDK (Virtual Disk Development Kit) during a read or write operation to a VMDK file.
Common causes that Veeam has found for this are:
- Corrupted VMDK
- Corrupted datastore
- Failing HBA controller
- Esxi host gets disconnected from vCenter for short periods of time
Due to the nature of this error a number of things may cause this error. If you are receiving this error it is advised to create cases with both Veeam and VMware to investigate.
A common factor is the use of the Network transport mode in Veeam. To determine which transport mode is being used by Veeam Backup & Replication review the statistics of the job, then click on the VM (see image below).
Veeam advises as part of troubleshooting this error that attempts be made to use a different transport mode. Such as Virtual Appliance or Direct Storage Access.
Veeam advises to clone or svMotion the VM to a different datastore, and then attempt to back up again. If a clone is performed, test a backup of the clone.
The cloning process that VMware performs recreates the VMDK content.
In some scenarios rebooting the source ESXi host where the VM resides can also resolve the issue
If the clone, svMotion, or host reboot process fails to produce a successful task, please contact VMware support.
If the backup of the clone is successful, attempt to migrate the production machine to the same storage or perform an offline clone during downtime and begin using the clone as the new production server.
Refer to this ESXi patch if ESXi disconnect issue is confirmed - https://kb.vmware.com/kb/2144799