vSphere vim.vm.guest.GuestOperationsManager APIs could be blocked during guest initiated Windows VSS freeze

Products

• VMware vCenter Server

Issue/Introduction

Symptoms:
When Windows VSS freeze is initiated by the guest instead of a quiesced snapshot operation through vSphere API vim.VirtualMachine method CreateSnapshot_Task(createSnapshot) / CreateSnapshotEx_Task(createSnapshotEx), a method call of vim.vm.guest.GuestOperationsManager could be blocked up to maximum 10 seconds that Windows VSS allows from FlushAndHoldWrites to ReleaseWrites.

Environment

VMware vCenter Server 6.0.x

Cause

This issue occurs when VMware Tools service process is blocked at file system write access when performing guest operation during Windows VSS freeze.

Note: This issue is observed in Windows guests with VMware Tools 9.4.x or later versions.

Resolution

To resolve this issue, VMware recommends leveraging vSphere API vim.VirtualMachine method CreateSnapshot_Task(createSnapshot) / CreateSnapshotEx_Task(createSnapshotEx) to perform Windows guest quiesced snapshot / virtual machine backup. vSphere API does not allow the vim.vm.guest.GuestOperationsManager APIs during quiesced snapshot operation.

To work around this issue when the guest Windows VSS freeze is not initiated by VMware vSphere API:

1. Open the tools.conf file in the Windows guest using a text editor as an administrator.
   
   Windows Vista, Windows 7, Windows Server 2008 and 2012:
   
   C:\ProgramData\VMware\VMware Tools\tools.conf
   
   Windows XP and Windows Server 2000/2003:
   
   C:\Documents and Settings\All Users\Application Data\VMware\VMware Tools\tools.conf
   
   
2. Change the following entries value to error:
   
   [logging]
   vmtoolsd.level = error
   vmsvc.level = error
   vmusr.level = error
   vmvss.level = error
   guestinfo.level = error
   vix.level = error

Notes:

• If the tools.conf file does not exist, create a new file and ensure to edit this file as an administrator.
• The Application Data/ProgramData folder is usually hidden. Ensure that hidden files are viewable.
• You must exercise caution when calling vSphere vim.vm.guest.GuestOperationsManager APIs during guest initiated Windows VSS freeze. For more information, see the Microsoft article Shadow Copy Creation for Providers.