Backups with Quiescing of the Operating System and Applications

Quiescing pauses or alters the state of running processes on a computer, especially those that might modify information stored on disk during a backup. Quiescing the operating system and file system helps to guarantee a consistent and usable backup that includes pending transactions.

Consider the following before enabling or disabling quiescing for backups:

  • VMware snapshot with quiescing - When you perform the backup of a subclient, quiescing is performed automatically for the operating system and applications on the virtual machines in the subclient. After quiescing, a software snapshot of all virtual machines for the subclient is created using VMware tools.  Backups may be slower with quiescing.
  • Crash consistent software snapshot - You can disable quiescing to create a crash consistent snapshot during the backup.

You can also perform an application aware backup as described in Agent Assisted Application Protection.

For virtual machines running Microsoft Windows, Volume Shadow Copy Service (VSS) inside the guest VM is used to quiesce the file system and applications. This ensures the data consistency of the file system and all VSS-supported applications. By default, VMware engages all VSS writers that are configured inside the guest. To exclude a writer, see Disabling specific VSS writers with VMware Tools (1031200).

For VMs running Linux, the vmsync driver included with VMware tools is used to quiesce the file system and applications.  The vmsync driver ensures that the file system is in a consistent state prior to the VMware snapshot being created. The vmsync driver is only supported with vSphere 5.0 and later.

If a virtual machine hosts a VSS-aware application such as Microsoft SQL Server, Microsoft Exchange, or Oracle, select the File System and Application Consistent option at the subclient level to provide the ability to back up the database and perform an image level application-consistent database recovery. The File System and Application Consistent option is enabled by default.

You can also call scripts to perform actions before and after backups. For more information, see Configuring Pre- and Post-Processing Scripts Using VMware Tools.


  • By default, when creating a snapshot on a VM, the file system and applications within the VM are quiesced. If the file system and applications cannot be quiesced, a non-quiesced snapshot is taken instead, and a warning is generated. When the requireSnapshotGuestFileSystem additional setting is configured on the VSA proxy with the value true, the automatic fall back to a non-quiesced snapshot is disabled and the backup of the VM fails.
  • To ignore quiesce failure errors for virtual machine backups, create the ignoreQuiesceGuestErrors additional setting on the Virtual Server Agent proxy and set the value to 1.