VMware Backups Fail | VMWARE_VMOMI1 Error | VSS Error 12289

Discover what to do if VMware backups fail with VMWARE VMOMI1 error and VSS error 12289. Our VMware Support team is ready to assist.

VMware Backups Fail | VMWARE_VMOMI1 Error | VSS Error 12289

VMware backups failing can disrupt our backup strategy and increase recovery risks. One common issue we may run into is the VMWARE\_VMOMI1 error, accompanied by VSS Error 12289 on the guest VM.

Today, we will explore the symptoms, root cause, and step-by-step resolution to get the backups working again.

About the Problem

When performing backups using VMware or third-party tools like Phoenix, we may run into the following issues:

• Backups fail with `VMWARE_VMOMI1` error.
• Manual snapshots get stuck at 100%, eventually timing out and failing.
• The guest virtual machine’s Event Viewer logs show:

  VSS Error 12289: Volume Shadow Copy Service error

  In the case of Phoenix VM backups, the failure message may appear as:

  An error occurred while saving the snapshot: Failed to quiesce the virtual machine.

  Additionally, logs may show:

  [ERROR] Error <class ‘pyVmomi.VmomiSupport.vim.fault.ApplicationQuiesceFault’>:(vim.fault.ApplicationQuiesceFault)
  message = ‘An error occurred while saving the snapshot: Failed to quiesce the virtual machine.’
  

These errors can be especially troublesome when managing agentless VMware backups, which rely on proper snapshot behavior for consistency. For a better understanding of agentless methods, check out this guide on agentless VMware backup.

Root Causes behind VMware Backup Failure

This error is usually due to conflicts between snapshot providers. The problem occurs when:

• A third-party snapshot provider overrides the Microsoft VSS provider.
• These providers interfere with the VSS quiescing operation during snapshots.
• The result is a failure to create a quiesced snapshot, which in turn leads to backup failure.

Step-by-Step Resolution

The VMware VSS provider, though installed by default with VMware Tools, is optional and can conflict with Microsoft’s VSS.
We can try disabling it to resolve the error.

Disable VMware VSS provider via GUI

1. Log in to the guest VM.
2. Go to Control Panel > Programs > Programs and Features.
3. Then, select VMware Tools > Click Change.
4. Now, choose Modify.
5. In the Custom Setup screen, expand Volume Shadow Copy Services Support.
6. Then, click the red X to disable this feature.
7. Now, complete the uninstall and reboot the system if prompted.

Disable VMware VSS provider via Registry Editor

Alternatively, we can manually remove the VSS provider:

1. Delete the folder:

   C:\Program Files\VMware\VMware Tools\Drivers\VSS
2. Now, open Registry Editor and delete the following keys:
   • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\vmvss
   • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\VSS\Providers\{564d7761-7265-2056-5353-2050726f7669}
   • Reboot the guest machine.

If the problem persists, and you suspect corruption in the VM files, it might help to recover the VMware VM from a flat file as a last resort before rebuilding.

Troubleshooting Tips

If snapshots continue to fail, follow these checks:

• Ensure the latest version of VMware Tools is installed on the guest VM.
• Make sure vStorage API and vCenter licenses are valid and not expired.

Even if the snapshot manager shows none, orphaned snapshot files might exist in the datastore. Use the datastore browser to verify.

• Check `vmware.log` for error messages like Error 3 or Error 5 during snapshot operations.
• Confirm required services like Microsoft VSS, VMware tools service are running. We can use `vssadmin list writers` to check writer states. Reboot the system if any are failed.
• Ensure there’s enough free space for VSS snapshots. Create a shadow copy on all drives with “No limit” selected for snapshot size.
• If problems persist, uninstall and reinstall VMware Tools to ensure proper configuration.

If you’re migrating between platforms or comparing hypervisors, understanding the differences between VMware vs Proxmox can help determine whether a more flexible snapshot handling solution is better for your environment.

Special Case: Windows Server 2019 with GPT Partition

VMs running Windows Server 2019 with GPT partition type may also show additional errors like:

Error in Deleting TL Files from streamset: Fileset/Streamset does not exist.
(Error Code: PHOENIX162)

To fix this, install the security update MS KB kb4534321 as suggested in VMware support articles.

[Need assistance with a different issue? Our team is available 24/7.]

Conclusion

The VMWARE_VMOMI1 and VSS Error 12289 are classic signs of snapshot provider conflicts. In most cases, removing the VMware VSS provider and ensuring a stable Microsoft VSS setup will resolve the issue.

In short, our Support Engineers demonstrated how to proceed if VMware backups fail with VMWARE VMOMI1 error and VSS error 12289