Steps for updating the XenServer PV drivers:
1. Login to CloudPlatform web interface.
2. Go to Instances and select an instance.
3. Click "Attach ISO" (paper clip icon)
4. Select "xen-pv-drv-iso" from the list and click OK:
5. RDP to the instance and install the drivers - login to the Windows OS.
6. Go to CD Drive in explorer and select XenServer:
7. Run the "xensetup.exe".
8. Once the installer has completed reboot now the machine, this step is mandatory in Windows. The installer may continue the installation and open back up after the reboot is complete.
9. After the installation has completed and the server rebooted, detach the ISO through CloudPlatform.
Now you should be able to attach/detach volumes on the fly without restarting Windows (volume hot plugging).