Online backups

When the Unitrends system initiates a backup of a virtual machine in a Hyper-V environment, the Unitrends agent creates a VSS-based point-in-time consistent snapshot of the Hyper-V host, which triggers a snapshot of the virtual machines on the host. If Integration Services are enabled, the appliance runs an online backup, and there is no downtime associated with the snapshot and backup of the virtual machine. The latest version of Integration Services must be installed in the guest operating system to perform backups in an online state. For a list of guest operating systems for which Integration Services is supported, see the Microsoft document Hyper-V Overview.

For the Unitrends appliance to successfully perform an online backup (child VM snapshot), the following conditions must be met on the protected VMs:

     The latest version of backup Integration Services must be installed and enabled.

     The VM’s VHD(x) files and snapshot file location must be set to the same volume in the host operating system.

     All volumes in the child VM are basic disks and there are no dynamic disks.

     All disks in the child VM must use a file system that supports snapshots (for example, NTFS).

If an online backup cannot be performed, the virtual machine is temporarily put in a saved state. In saved state there is a brief downtime associated with the backup process. It is important to understand that if a VM does not have Integration Services installed, the backup job can cause the virtual machine to be inaccessible to connected users for a short period of time (less than a minute).