openmediavault-usbbackup is a core OMV plugin that backs up to or from a usb drive when it is plugged in.
openmediavault-backup is an omv-extras plugin that can backup the system drive to a data drive, allow booting from multiple ISOs (clonezilla, systemrescuecd, partedmagic, gparted live), and has undelete utilities (photorec, extundelete).