Hyper-V 2019 Host Crashes During Backup Operation

If CBT is disabled on a Virtual Server Agent (VSA) subclient, the backup uses CRC with VSS, which might cause a Hyper-V 2019 host to crash.

Symptoms

During a backup operation, the Hyper-V host may crash under the following conditions:

• Virtual machines being backed up are on a Hyper-V 2019 host.
• Changed Block Tracking (CBT) is disabled on the VSA subclient for the backup.
• The VSS Legacy Tracing feature is enabled on the host.

Causes

When CBT is disabled on the VSA subclient, the Virtual Server Agent tries to perform the backup using CRC (Cyclic Redundancy Check) with Volume Shadow Copy Service (VSS).

If the VSS Legacy Tracing feature is enabled on a Hyper-V 2019 host, this operation may cause the host to crash. This feature is deprecated and should not be used on Hyper-V 2019 hosts.

Resolution

To resolve this issue, disable the VSS Legacy Tracing feature on the Hyper-V 2019 host using either of the following methods:

• Modify the HKLM\SYSTEM\CurrentControlSet\Services\VSS\Diag registry key and change the value from Default to Disabled.
• Run the following PowerShell command:

Set-ItemProperty -Path HKLM:\SYSTEM\CurrentControlSet\Services\VSS\Diag -Name "(Default)" -Value "Disabled" –PassThru