How to resolve the backup error 'An error occurred while quiescing the virtual machine'

How to resolve the backup error 'An error occurred while quiescing the virtual machine'


A VMware backup job may fail with the following error message:

An error occurred while quiescing the virtual machine.

As this issue is primarily one with VMware technology it is difficult for Infrascale to identify and resolve the problem. In this article, we have provided some potential resolutions as well as some last-resort workarounds. We strongly recommend, however, that you reach out to VMware support for a permanent solution if all of the potential resolutions do not work. 

What is Quiescing?

Quiescing a file system is a process of bringing the on-disk data of a physical or virtual computer into a state suitable for backups. This process might include such operations as flushing dirty buffers from the operating system's in-memory cache to disk, or other higher-level application-specific tasks.

This VMware technology allows the creation of application-consistent backups. If the VMware snapshot with quiescing enabled has failed, it means that the VSS snapshot for the guest OS of the VM failed.

You can find additional information about VMware Snapshots in the following article:
Overview of virtual machine snapshots in vSphere (1015180)

Potential Resolutions

VMware Tools

VMware Tools is used to quiesce the file system in the virtual machine. Because of this, VMware Tools must be installed, up to date, and running in order for quiescing to function properly.

You can find the steps on how to install VMware Tools in the following article:
How to install VMware Tools (1014294)

Free Space on the VM and VSS Shadow Storage

In order to run a VSS snapshot, the VM should have enough free space on both the disks and inside VSS Shadow Storage. Check that the VM has at least 15% of free space on the disks and VSS Shadow storage.

You can find the steps on how to check the space in VSS Shadow Storage, increase the size of the VSS Shadow Storage, or remove old VSS Shadow Copies in the following article:
How To Resolve an 'Insufficient Storage Space' Error

Reboot the VM or Restart the VSS services

In some cases, the services may be stuck on the VM. It is recommended to try rebooting the VM to make sure that there are no frozen processes. Another approach is to try restarting the VSS services manually.

You can find additional troubleshooting steps published by VMware in the following article:
Troubleshooting Volume Shadow Copy (VSS) quiesce related issues (1007696)

Articles created by VMware

There are a few additional KBAs provided by VMware regarding this error:


Shut down the VM before running a backup

If the VM is not running, quiescing is not needed. The reason for this is that all the data is on the disks and no data is present in the cache or RAM. Shutting down a VM and running a manual backup job should succeed but require you to shut down the VM every time you would like to run a backup.

Disable Quiescing

This approach is NOT recommended by the Infrascale team unless it is a last resort.
It is possible to disable the option "Quiescing" on the appliance UI on the Clients → Edit tab. This will stop doing VSS snapshots inside the VM guest OS. The backup job will succeed but will be crash-consistent instead of application-consistent, which means that live data that is in the RAM and cache will not be backed up.