Full VM backups of UC VMs are never guaranteed to restore, due to quiescing dependencies. Application-consistent Full VM backups are most likely to successfully restore. Crash-consistent full VM backups are less likely to successfully restore.
Full VM backups of live UC VMs are statistically likely to be application-consistent, but they may only be crash-consistent. Full VM backups of powered-down VMs are always application-consistent.
The Cisco DRS backup feature is designed to properly back up the UC applications, and it should always be used as the most fail-safe method to restore a UC application instance. Full VM backup is not a replacement for Cisco DRS, so customers should continue to take Cisco DRS backups.
Cisco DRS backups or other UC application-specific backups should continue to be taken on a regular basis.
Full VM backups, with very high likelihood, can be used to restore the UC application instance, but there is no guarantee. This is why the Cisco DRS backup should always be done as an alternative way to restore the UC instance. Cisco recommends that any full VM backups should be made while the VM is powered off. But testing has shown a high likelihood that crash-consistent backups can be used successfully as well. If taking crash-consistent backups, Cisco recommends you take them during a low-traffic period to minimize the possibility that the application is negatively affected by the backup.
If customers choose to perform full VM backups, they must test the restoration process first to ensure that the method they are using works to restore both the cluster and individual application instances. Cisco does not test or validate any specific full VM backup methods. The customer chooses the method and tests it. It is very likely the customer will have to manually synchronize the database when restoring a cluster.
Ultimately, Cisco cannot guarantee that by following these guidelines any full VM backups can be used to successfully restore a UC application instance. If a full VM backup cannot be used to restore the VM, the only recourse is to reinstall the application and restore via Cisco DRS backup instead.
Statistically, using VDR, it is possible to back up a virtual machine reliably. The memory cache not written to disk does not seem to affect the outcome of a restore. The backups taken by VDR generate no noticeable errors over the course of time. No errors were observed after a restore of an active server. There is minimum impact to call processing during the VM backup.