On a computer that is running Windows Server 2008 R2, Hyper-V VSS Writer waits for the migration to complete before continuing a backup when a live migration is in a transition state. As soon as the migration is complete, the virtual machine is removed from the node that the backup is occurred on. The backup continues and correctly backs up the files and the backup can still access the files on the Cluster Shared Volumes (CSV) volume. However, it is not a real file copy. The Hyper-V VSS writer does not perform as expected during an online backup.
You may see one or more of the following error messages that relate to the Hyper-V VSS Writer:
You may see one or more of the following warning messages in the Hyper-V VMMS Admin log:
Cannot find the specified virtual machine. (Virtual machine ID [VMGUID])
The virtual machine '[VMName]' cannot start a backup operation because it failed to change its state. Try the backup again. (Virtual machine ID [VMGUID])
This problem occurs when the backup is about to start or when the backup has just started. An error message is displayed only after the Hyper-V VSS writer returns an error code to VSS which the requestor receives. Additionally, one or more failure or warning messages are logged in the Virtual Machine Management service (VMMS) Admin event log.
Note The check for transition state is not the first step of a backup.
To work around this problem, do not run the backup and live migration at the same time. We recommend that you run one operation completely and then start the other.