vDR and Quiescing Mechanisms

It appears that looking closely at the vDR capabilities, there are different level of quiescing mechanisms supported by VMware Data Recovery (vDR) and unfortunately VMware Data Recovery doesn’t support a lot of them for Windows OS’es.

First let’s review those mechanisms:

  1. Crash-consistent quiescing. That is, the image is equivalent to the image left on the system if the power is unexpectedly cycled. Some transactions in progress may not complete. In addition, image-based backup does not allow for file-based restoration.
  2. File-system consistent quiescing. That is, VMware will quiesce the file systems (only for Microsoft® Windows virtual machines). This ensures that no file system writes are pending at the time the snapshot is taken, allowing the creation of file-system consistent backups.
  3. Application-consistent quiescing. That is when VMware tells the application that is has been backed up so that it can clear its transaction logs.

Now in the VMware Data Recovery Admin guide we can read that vDR uses different quiescing mechanisms depending on the guest operating system that you run in your virtual machines.

‘VMware obviously can back up a Windows volume via VSS.  However, its support for applications is sadly lacking.  It can only quiesce applications if they happen to be running on a Windows 2003 guest, and it cannot tell any of the applications they have been backed up.’ says W. Curtis Preston on his blog, and it’s no FUD here….

Yes, true, VMware requires third party agent to properly do application-consistent backups for Microsoft newest operating systems, that is Windows Vista, 2008 and 2008 R2 and W7, running application that use transaction logs i.e. Microsoft SQL and Microsoft Exchange. Although, there is a workaround, like using scripts located in C:\Program Files\VMware\VMware Tools\backupScripts.d  to stop applications before backing them up, and to restart them after backup is complete, this is IMO middle-age practises!

Did VMware try to hide this? Not at all, it is clearly written in the vDR admin guide.
Is this issue a problem in your environment? I would like to hear it from you.


About PiroNet

Didier Pironet is an independent blogger and freelancer with +15 years of IT industry experience. Didier is also a former VMware inc. employee where he specialised in Datacenter and Cloud Infrastructure products as well as Infrastructure, Operations and IT Business Management products. Didier is passionate about technologies and he is found to be a creative and a visionary thinker, expressing with passion and excitement, hopefully inspiring and enrolling people to innovation and change.
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5 Responses to vDR and Quiescing Mechanisms

  1. deinoscloud says:

    There are 2 other great posts I wanted to share with you regarding backups and VSS and future of VMware quiescing mechanisms.



  2. deinoscloud says:

    A great post from VirtualKenneth regarding LeftHand VM snapshot mechanisms and quiescing -> http://virtualkenneth.com/2010/02/27/using-lefthand-snapshot-techniques-within-a-vmware-environment/

  3. Pingback: VMware vSphere Fast Track Day#5 – Lessons Learned « DeinosCloud

  4. Hello,

    I think you should revisit VDR – since VDR 1.2 application-level consistent VSS snapshots are possible (see the VDR 1.2 admin guide).

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