In the Solutions Lab, we are always looking for ways of improving virtual machine density per blade, from OS-related settings to hypervisor tuning. While it’s known that disabling USB and DVD drive gives more density, we have used the new enhanced feature in XenServer to do so from the hypervisor, and we are going to show you how it’s done. We are also going to highlight the performance gains we saw in our tests with our single-server environment utilizing Cisco UCS B200M3 blades.

 How to disable guest USB emulation and DVD drive on XenServer 6.2

XenServer 6.2 made enhancements to make it easier to disable USB and DVD drive via the hypervisor, plus giving us the ability to create scripts for it.  In previous versions of XenServer (6.1 and older), it has been documented that disabling the guest VM USB controller improved density  (http://support.citrix.com/servlet/KbServlet/download/35495-102-705709/WP_XS6.1_Scalability_Disable_USB.pdf).  This procedure involved making modifications at the VM guest client OS level and is specific to the type of Windows operating system.

Disabling the USB controller affects the performance of keyboard and mouse control over the XenCenter VM console. The VM console is still functional after disabling USB, and it’s not a common way of managing the virtual machine. This is a great tradeoff because you can instead manage the VM through remote services, such as RDP, or present it as a hosted virtual desktop, as was the case in these tests. We find the use of the console through XenServer for VMs to not be a priority because the purpose of the desktop VM is to be delivered with high performance and usability through Citrix Receiver.

The DVD drive can be disabled after the initial OS and XenServer tools installation.

We used the XenServer 6.2 command line to modify each VM’s parameters. The command is applied to each VM individually. Prerequisites are to have the VM in powered-off state and find the UUID of the virtual machine to modify.

Disable USB emulation:

xe vm-param-set uuid=<uuid> platform:usb=false

xe vm-param-set uuid=<uuid> platform:usb_tablet=false

Disable DVD drive:

xe vm-cd-remove uuid=<uuid> cd-name=xs-tools.iso

To apply these commands to all the virtual machines on the XenServer 6.2 host, we used the following:

for vms in $(xe vm-list is-control-domain=false is-a-template=false is-a-snapshot=false | grep uuid | awk ‘{print $5}’)

do

xe vm-param-set uuid=$vms platform:usb=false

xe vm-param-set uuid=$vms platform:usb_tablet=false

xe vm-cd-remove uuid=$vms cd-name=xs-tools.iso

done

Test configuration and results

The following hardware and software components were used to perform the tests:

Cisco UCS B200 M3 blades with Intel® Xeon® E5-2697 v2 (“Ivy Bridge”) processors, 384GB (1333 MHz) memory, Citrix XenDesktop 7.1, Citrix Provisioning Services 7.1, XenServer 6.2SP1, Login VSI 3.7 software from Login VSI Inc. (http://www.loginvsi.com), Remote (NAS) shared storage using NFS for Infrastructure Storage.  Storage was oversized to eliminate it as a potential bottleneck and focus on the physical server.

The hosted virtual desktop master image has the following configuration: 1vCPU, 1.5 GB RAM, 30 GB vDisk size, 3 GB write cache, one virtual NIC, Windows 7 32-bit, Login VSI 3.7 target software, Microsoft Office 2010, Citrix XenDesktop VDA agent and Citrix Provisioning Services target device.

We used Provisioning Services 7.1 XenDesktop Wizard to deploy 200 Virtual Machines for hosted virtual desktops.

hosted virtual desktops (base configuration, with USB and DVD drive) Single Server VSI Max Results

VSImax corrected=167 (uncorrected=167)

Dynamic VSImax = 4496

Baseline= 1197

hosted virtual desktops (USB and DVD drive disabled on each VM) Single Server VSI Max Results

 

VSImax corrected=175 (uncorrected=175)

Dynamic VSImax = 4444

Baseline= 1155

Conclusions

The new enhancements to XenServer 6.2 gives us the ability to disable the USB controller and DVD drive on guest VMs easily without having to modify the guest OS. We can streamline these tasks by creating scripts. Test results show that after disabling USB and DVD, we get a better Login VSI Max score and slightly better response time.