Disabling write caching in guest VM - recommendations?

[DrSheldonCooper]

Hi folks

We're using a few different technologies which rely on VMware snapshots to take backups and/or copies of our Windows virtual machines (let's stick with NetBackup for the purposes of this discussion)

The backup software hooks into vCenter and requests that it trigger a snapshot of the VM. The backup software then copies the snapshot and finally requests that vCenter delete the snap. Easy-peazy.

These are crash-consistent backups. If I ever have to restore a complete VM, when I power it up, the guest OS (Windows) will act as though it had experienced an unexpected shutdown.

My question is regarding the implications of the "policy" setting in the properties of a disk in Windows, and of changing this policy to disable write caching. I would think that this would be desirable for any machine where I'm taking these backups, because it means that the guest OS will dump everything to disk immediately, thus reducing the potential for corruption / data loss in the event that I have to recover a machine from one of these backed up snapshots.

I did a lot of Googling on this topic but haven't seen anything which really addresses it from this angle

Thoughts?

[a_p_]

Welcome to the Community,

what you describe (i.e. the guest flushing data to disk) is Windows' VSS feature, that's triggered by backup applications prior to creating the snapshot to avoid data loss. So there's no need to disable caching in the guest OS, which would most likely have an impact on performance.

André

[riahc3]

For me in WS2012R2 the policies tab does not show up....

[Alistar]

You can try somewhat reducing the VM's IO either manually or by scripts before the backup takes place so you have much bigger chances of successful quiesced snapshot and subsequent backup.