This will be an example of how to backup your system drive headless, meaning no monitor attached to your OMV. Before doing this you should setup a static lease for your OMV in your router settings. I will make another post and provide a link on how to setup a static lease for your OMV for DD-WRT. This way your OMV will always be assigned the same IP address when booting to an ISO disk like Clonezilla.
1) First you need to make a backup folder on one of your data drives:
2) Go to the plugin section and install openmediavault-backup plugin
3) Then go to System/Backup and then click the Clonezilla TAB on the right. (See Pic1)
4) Click on the Install butoon. This will download the latest Clonezilla ISO to your /boot folder on the system drive. (Pic1)
5) Click on Clonezilla button. The will set grub to boot to the Clonezilla ISO one time. (Pic1)
6) Then click on reboot. (Pic2)