If you protect your Hyper-V hosts with Veeam Backup & Replication, you could find an issue during backup job of one, or more, virtual machine. This issue is generated by VSS Writer on Windows Server, as showed in figure 1. The full message error is:
Unable to allocate processing resources. Error: Writer ‘Microsoft Hyper-V VSS Writer’ is failed at ‘VSS_WS_FAILED_AT_PREPARE_SNAPSHOT’.
The writer experienced a transient error. If the backup process is retried,
the error may not reoccur.
–tr:Failed to verify writers state.
–tr:Failed to perform pre-backup tasks.
Checking the Hyper-V Manager console is possible see that the VMs are in a “hold state”, as showed in figure 2.
This happen when the old snapshot are not consolidated from VSS Writer. The resolve this problem is necessary restart the service Hyper-V Virtual Machine Management; is not required stops the production activity. After restart the VM’s state will change, as showed in figure 3.
Now is possible run again the backup from Veeam console and if is all ok, the job progress will be similar figure 4.