StartBackupSession failed. error: Create snapshot task failed: An error occurred while quiescing the virtual machine

Symptoms

The error is reported during backup (VMware VADP backup sets).

Cause

1. As per VMware KB 2069952, the Virtual Disk service does not start in the Windows guest operating system on the affected virtual machine.

2. The issue might also be encountered if running into the scenario described in VMware KB 1018194, it occurs when the I/O in the virtual machine is high and the quiescing operation is unable to flush all the data to disk, while further I/O is created.

This issue also occurs if you try to create a quiesced snapshot on a virtual machine that does not have free space. That is, if the free space on the virtual machine is 0 bytes.

3. Other VMware KBs related to creating snapshot failure:
2068653 - Quiesced snapshots fail on a Windows Server 2012 virtual machine with Microsoft Exchange 2013
2015181 - Creating a quiesced snapshot of a Windows 2008 virtual machine fails with the error: "Snapshot 0 failed: Failed to quiesce the virtual machine"
1031298 - Cannot take a quiesced snapshot of Windows 2008 R2 virtual machine. 

Solution

1. To resolve this issue, start the Windows Virtual Disk service:

a) Log in to the Windows operating system as an Administrator.
b) Click Start, type services.msc, and click Enter.
c) Right-click the Virtual Disk service and click Start.

2. The workarounds are provided in the VMware KB 1018194:
http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1018194

- The issue occurs if any of the VSS writers are failing. Verify the list of writers before running the backup job and after the job is finished, verify if any VSS writer is failing. As the VSS writers are provided by third-party vendors, engage the vendor for any issues with them or to troubleshoot any failures of those writers.

- Reduce the amount of ongoing I/O to the virtual machine. This is accomplished using pre-freeze scripts or post-freeze scripts to quiesce application I/O.

- Opt for a crash-consistent snapshot (as opposed to application-consistent) of the virtual machine by avoiding quiescing of the file system (deselect the option "Attempt to quiesce I/O before taking snapshot" in DS-User backup set's properties, options tab).

3. Apply the recommendations available with the VMware KBs related to creating snapshot failure:
2068653 - Quiesced snapshots fail on a Windows Server 2012 virtual machine with Microsoft Exchange 2013
2015181 - Creating a quiesced snapshot of a Windows 2008 virtual machine fails with the error: "Snapshot 0 failed: Failed to quiesce the virtual machine"
1031298 - Cannot take a quiesced snapshot of Windows 2008 R2 virtual machine.