http://wiki.qemu.org/Features/Livebackup
How to use Livebackup to create incremental backups of virtual machines in proxmox?
The goal of this project is to add the ability to do full and incremental disk backups of a running VM. These backups will be transferred over a TCP connection to a backup server, and the virtual disk images will be reconstituted there. This project does not transfer the memory contents of the running VM, or the device states of emulated devices, i.e. livebackup is not VM suspend.
How to use Livebackup to create incremental backups of virtual machines in proxmox?