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Monday, December 21, 2015

Explain about VSS writers in Virtual Machines and how to disable the specific VSS writers with VMware Tools

VMware products may require file systems within a guest operating system to be quiesced prior to a snapshot operation for the purposes of backup and data integrity.
VMware products which use quiesced snapshots include, but are not limited to, VMware Consolidated Backup and VMware Data Recovery.
As of ESX 3.5 Update 2, quiescing can be done by Microsoft Volume Shadow Copy Service (VSS), which is available in Windows Server 2003.

Operating systems which do not have VSS make use of the SYNC driver for quiescing operations. When VSS is invoked, all VSS providers must be running. If there is an issue with any third-party providers or the VSS service itself, the snapshot operation may fail.
Before verifying a VSS quiescing issue, ensure that you are able to create a manual non-quiesced snapshot using the vSphere Snapshot Manager.

With vSphere 4.0, VMware introduced the ability to disable specificVSS writers for the benefit of troubleshooting a specific VSS writer issue.

If you experience an issue backing up a specific virtual machine using snapshot technology and you have identified an issue with a specific VSS writer within the virtual machine, this blog  explains how to disable that VSS writer from being called during a snapshot operation.

To disable a specific VSS writer being called during a snapshot operation:

    Determine the name of the VSS writer that you want to exclude from the snapshot operation. Run this command from within Windows:
    vssadmin list writers
    Note: With Windows Vista, 7, and 2008 the command prompt may need to be run with administrator elevation.

    You see output similar to:

    Writer name: 'Task Scheduler Writer'
       Writer Id: {d61d61c8-d73a-4eee-8cdd-f6f9786b7124}
       Writer Instance Id: {1bddd48e-5052-49db-9b07-b96f96727e6b}
       State: [1] Stable
       Last error: No error
    Note: The name of the VSS Writer is highlighted.

    Create or edit the vmbackup.conf file which is located at %ALLUSERSPROFILE%\Application Data\VMware\VMware Tools\ .

    Note: If the vmbackup.conf file does not exist then create it.
    Place the name of the VSS writer you want to disable on a separate line. If you want to disable more than one VSS writer, ensure that you place each VSS writer name on a separate line. For example:
    Task Scheduler Writer
    Microsoft Exchange Replica Writer
    Microsoft Exchange Writer
    Restart the VMware Tools service.
    When the writer issue has been resolved, you can remove the offending writer from the vmbackup.conf file.

Note: VMware does not provide these VSS writers. Engage the provider of the VSS writer to troubleshoot the writer issue to ensure application consistency with the writer.

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