This article explains how to backup a virtual hard disk to a remote location, even while it is use.
One advantage of running software in a virtual machine is that the entire disk can be backed up in one go, including Operating System, software, configuration files, registry, permissions, data and all. Re-establishing a system after a failure is therefore quicker and more reliable than re-installing software and restoring data.
The method employs LVM to take a snapshot of the guest disk and then uses rsync to update changes to a previous backup on a remote server. If there is a database server on the guest then it is flushed & locked at the point the snapshot is taken. This method came into use around 2008 following wider availability and awareness of virtualization software, cheaper faster network bandwidth, and cheaper bigger disks.