During backup, if the snapshot was created with quiesce flag set to true, and all the quiescing conditions are met, so the snapshot is created involving VSS and the snapshot disks represent application consistent state of the guest OS. You should be able to confirm this by downloading the VSS

manifest zip

file, unzipping it to check if it has just the backup component document (in which case file system quiescing was performed) or also writer manifests (in which case application quiescing was performed).

Quiescing involves the VSS mechanism designed by Microsoft. So, regarding VSS backup-restore verification, refer to the VSS documentation provided by Microsoft. VMware helps by providing a

vss-manifest.zip

file that contains Backup/Writers Components details. This is generated by the VSS mechanism after backup. By cross verifying these backup/writers components details according to Microsoft VSS documentation, you can verify if a particular application-consistent quiescing was completed successfully or not.

VMware Tools is responsible for initiating the VSS snapshot process as the VSS requester. Users send a request to

hostd

for a quiesced snapshot of the virtual machine. The request goes from

hostd

to the VMware Tools for a VSS snapshot. Once the VSS snapshot is completed (with success or error) it communicates back to the

hostd

process. The VSS snapshot is created with the

vss-manifest

file, or without this file in the error case.

The VSS requester sets up the overall configuration for the backup operation, including whether the snapshot should be performed in component mode or not, whether to take a snapshot with a bootable system state, and whether the snapshot should be for a full copy or differential backup. If application-consistent quiescing is performed, then all writers and all components are involved.

VMware Tools initiates VSS quiescing using

VSS_CTX_BACKUP

context for application quiescing capable guests with backup state set to select components, backup bootable system state with backup type

VSS_BT_COPY

and no partial file support and

VSS_CTX_FILE_SHARE_BACKUP

for file system quiescing capable guests. Currently there is no way to control any of these parameters.