Due to various customer support issues we have decided to disable disk hotplug in the 3.0 GA refresh until further notice. This is due to various hardware configuration issues that were not envisaged at the time of development. Once these configurations have been fully tested it will be re-enabled at a later date.
This affects both KVM and Xen.
Update - Disk Hotplug support has been added via the 'diskhotplug' CLI command in OnApp 3.1.2