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© XSIBackup: troubleshooting Windows snapshots in ESXi

We dedicated a post to snapshots from a generalist point of view some time ago. It covered the matter from a wide angle and was focused in how to rebuild a broken chain of snapshots. Nevertheless the problems related to snapshots vary from one Operating System to another. Each system has it's particularities, and Windows OSs are among the most picky to configure.

Windows is yet by far the most used OS for desktops and is also used as a server OS by many people and organizations.

This article applies to relatively recent OSs:
- Windows Server 2008
- Windows Server 2008 R2
- Windows Server 2012
- Windows Server 2012 R2
- Windows Server 2016
Older Windows releases, prior to VSS (Volume Shadow Services) used what's called the SYNC Driver from VMWare, but we will not cover those OSs in this post as their use is marginal nowadays.

Quiescing your OS consists in orchestrating services' behaviour during the snapshot operation, so that they finish to write whatever data they are still processing in their buffers before actually taking the snapshot. Once the snapshot is taken, they continue to write data to it, but the state of the database or e-mail files is consistent at a given point in time. It's actually inevitable to perceive a little pause in service performance during the snapshot creation.

Snapshots are the most critical operation in VMWare ESXi backups. They are required to free the data disks and be able to back them up. If on addition you need to backup your servers while they are active, you will need to take a quiesced snapshot. XSIBackup does this by default, but it requires that you take some actions and ensure your OS is tweaked for quiescing to be possible.

XSIBackup philosophy is to allow ESXi servers to become independent in terms of protecting their data. Even if a hypervisor get's disconnected from the rest of its infrastructure, it should be able to back it up. Thus, in case a quiesced snapshot cannot be taken, XSIBackup will try to automatically work the flaw around by taking a non-quiesced snapshot, even if some data could eventually get corrupted under a high load, at least you will have a backup.

In order to quiesce a Windows OS properly, you need some services installed and configured the right way, otherwise the quiescing operation could fail with a number of error messages like:
- Create snapshot failed

- Cannot create a quiesced snapshot

- Failed to create snapshot for vmname, error -3960 (cannot quiesce virtual machine)

- Cannot create a quiesced snapshot because the snapshot operation exceeded the time limit for holding off I/O in the frozen virtual machine

- An error occurred while quiescing the virtual machine. The error code was: 4 The error was: Quiesce aborted

What are those services and how should I configure them?:

First of all you need latest VMWare Tools installed in your Windows Server system. You can install them from the vSphere Client, no matter if you are using the Windows client or the HTML5 GUI

VSS related components are installed by default. In any case check that you are not leaving some vital component out of the installation process, especially if you are running some older ESXi version.

You do need the following services in the mentioned state:

Service State Startup
Volume Shadow Copy Idle Manual
Microsoft Software Shadow Copy Provider - Manual
VMware Snapshot Provider - Manual
COM+ System Application Started Manual
COM+ Event System Started Automatic
Virtual Disk - Manual


Make sure that all above services are installed and configured as described. Review all system logs to make sure none of the above mentioned services is failing or throwing some error/warning.

Some Windows services like SQL Server or Exchange have their own auxiliary VSS services, which must be properly configured to be able to quiesce Windows servers running them. Review the product's specific documentation to learn more about how to configure those VSS auxiliary services.

For more detailed information visit this VMWare post.



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