vzdump is an utility to make consistent snapshots of running OpenVZ VEs. It basically creates a tar archive of the VE private area, which also includes the VE configuration files.

There are several ways to provide consistency:

• stop the VE during backup (very long downtime)
• use rsync and suspend/resume (minimal downtime)
• use LVM2 (no downtime)

Taken from proxmox.com.