I have an error from a Veeam Hyper-V backup of a Virtual Machine in a Hyper-V host:
Unable to create snapshot (Microsoft CSV Shadow Copy Provider) (mode: Veeam application-aware processing). Details: Writer 'Microsoft Hyper-V VSS Writer' is failed at 'VSS_WS_FAILED_AT_POST_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 create VSS snapshot. --tr:Failed to perform pre-backup tasks.
I cannot understand if this is a host error, a guest error or Veeam error. I tried to reboot the VM but I got the same error. I did not try to reboot the host, but I tried to change the host (this VM is inside a failover cluster of two hosts) and with this change the backup works again.
During the backup failure I ran this command in the host:
vssadmin list writers
The output was:
> Writer name: 'Microsoft Hyper-V VSS Writer'
> Writer Id: {66841cd4-6ded-4f4b-8f17-fd23f8ddc3de}
> Writer Instance Id: {f50fe40b-27d6-4a98-8713-e5a1dce54c97}
> State: [1] Frozen
After the VM migrates to another host, the writer state changes back to "Stable".
What can freeze the VSS writers?
There is a 10103 event in the Host:
Failed to revert to VSS snapshot on the virtual hard disk '\\?\Volume{29e16157-002f-4cb4-af58-c95acbd54be9}\' of the virtual machine 'srvshare1'.