Problem Description
Hyper-V virtual machine backups fail consistently during the snapshot creation phase, preventing the backup from completing successfully.
Associated Error Codes:
Phoenix54
Phoenix168
Symptoms
Hyper-V VM backups fail repeatedly during snapshot creation.
The Hyper-V VSS writer enters a Failed or Timed Out state.
Multiple system VSS writers show unstable behavior.
Example Log Errors:
Microsoft Hyper-V VSS Writer reported status: [9] Failed / Timed Out [2026-03-26 22:37:57,157] [ERROR] SyncError: VSS snapshot operation 'DoSnapshotSet' failed/timedout.
Cause
The failures stem from the Microsoft Volume Shadow Copy Service (VSS) on the Hyper-V host. Common contributing factors include:
Hyper-V VSS Writer or System Writer failing/timing out.
Conflicting or orphaned third-party VSS providers.
Outdated VM configuration versions (e.g., Version 5.0): Older configuration versions do not natively support modern Resilient Change Tracking (RCT) workflows, forcing the agent to rely on traditional, less stable VSS-based backup methods.
Validation Steps
Step 1: Check VSS Writers
Run the following command in an elevated Command Prompt on the Hyper-V host:
vssadmin list writers
Verify that Microsoft Hyper-V VSS Writer and System Writer reflect:
State: [1] StableLast error: No error
If they display State: [9] Failed or State: [8] Timed Out, the VSS subsystem is unstable.
Step 2: Check VSS Providers
Examine the host for orphaned or conflicting third-party VSS providers by running:
vssadmin list providers
Step 3: Verify VM Configuration Version
Run the following PowerShell command to identify the configuration versions of your VMs:
Get-VM | Select Name, Version
Note: Legacy versions (like 5.0) must be upgraded to leverage modern RCT functionality.
Resolution
The definitive solution is to upgrade the legacy VM configuration and transition the backup method from traditional VSS snapshots to Resilient Change Tracking (RCT).
Step 1: Upgrade the VM Configuration Version
Identify supported versions on your host:
Get-VMHostSupportedVersion
Upgrade the specific VM configuration version:
Update-VMVersion -Name "YourVMName"
⚠️ Important: VM configuration upgrades are irreversible. Ensure the VM is powered off (if required by your OS version) before running the upgrade.
Step 2: Benefits of Shifting to RCT
By upgrading to Windows Server 2016 or later and updating the VM configuration version, Druva automatically utilizes RCT. This provides:
Significantly reduced dependency on host-level VSS snapshots.
Faster, highly stable incremental backups.
Better resiliency against target failure states.
Step 3: Reconfigure the VM in Druva
Log in to the Druva Management Console.
Navigate to Protect > Hyper-V > All Virtual Machines.
Click the Refresh icon to force a rediscovery of the newly updated VM configuration.
Navigate to Protect > Hyper-V > Configured VMs.
Select the affected VM, click the three dots (ellipsis) menu, and select Reconfigure VM if prompted.
Trigger an on-demand backup to validate success.
Additional Recommendations
Keep Integration Services Updated: Ensure Hyper-V Integration Services are updated inside the guest OS.
Service Restarts: If VSS writers remain unstable, restart the following services via
services.msc:Volume Shadow Copy Service (
VSS)Hyper-V Volume Shadow Copy Requestor
Antivirus Exclusions: Verify your security software excludes the following Hyper-V file extensions:
.vhd,.vhdx,.avhdx, and.rct.