Hyper-V Guest Quiescence - understanding

[check4backup]

Hello,

i do not understand the Hyper-V Guest Quiescence. I have only Windows guests. All of them support VSS.

Application Aware
Whenever I have a guest with a DB (SQL) I use Application Aware. Everything is fine. I determine if I want to have a "only copy backup" or not.

Guest Quiescence
Until now, I thought that if I didn't use Application Aware, I *must* turn on Guest Quiescence. Now I'm thinking that this won't hurt, but it won't help either because I only have Windows guests and they all support VSS.

Do I think right or wrong here?

When do I need Hyper-V Guest Quiescence with Windows guests? Never?

Best regards

[moustafa_hindawi]

To create transactionally consistent backups and replicas for VMs that do not support Microsoft VSS (for example, Linux VMs), you must enable Microsoft Hyper-V guest quiescence for the job.

[check4backup]

That's a quote from the documentary, that's what I read.

[PetrM]

Hello,

You need to enable the quiescence even for Windows-based VMs if you don't use AAIP. The reason is that without quiescence the volume snapshot is created without any writers involved, therefore Hyper-V VSS writer on host does not send a command to trigger VSS activity inside the VM (the volume snapshot is created with NO_WRITERS flag).

The sentence from the help center just represents the main case (VMs without VSS) when quiescence must be used but I agree that it's a bit ambiguous.

However, I'm wondering why you don't use AAIP for Windows VMs? It's highly recommended to enable it whenever possible even if you have no specific applications, there are still OS (f.g. registry, system, WMI) and file system VSS writers that help to produce the consistent image of the VM. Just run "vssadmin list writers" command in the guest VM.

Thanks!