XenDesktop 7 is the latest product release from Citrix for delivering virtual desktops and applications allowing users to work from anywhere on any device.  XenDesktop 7 is supported on all the major hypervisors; however I will present the case for selecting Hyper-V 2012.  Please note, that this will not be a Hyper-V versus VMware or XenServer hypervisor comparison.  Each hypervisor offers unique features that organizations will have to decide which is most important to them.  However Hyper-V 2012 offers some great enhancements over Hyper-V 2008 R2 for XenDesktop 7 deployments.

1.      Support for Windows 8 and Windows 2012 Virtual Machines

Hyper-V 2012 supports Windows 8 and Windows 2012 virtual machines.  This may not be important for organizations with existing Windows 7 VDI deployments, but those running Windows XP should take notice. Microsoft has announced that all support for Windows XP will end next year on April 8, 2014.  As of April 2013, NetMarketShare research shows that Windows XP is the second most widely used desktop operating system for businesses with 38% of the market share.  Windows 7 is in first place with 44% market share.

NetMarketShare research also shows that over a period from Sept 2012 to April 2013, Windows 7 market share has remained steadfast at 44%. Windows XP market share has declined from 41% to 38%, while Windows 8 grew from 0.8% to 3%. If the current trend continues, most organizations with Windows XP VDI deployments will be migrating to Windows 8.  XenDesktop 7 will support all versions of Windows desktops from Windows XP to Windows 8, so organizations can leverage it for migrations, and continue to support legacy applications that won’t run on Windows 8.

2.      SMB 3.0 Enhancements

The Server Message Block (SMB) protocol is used for file sharing in Windows. In Windows Server 2012, the SMB protocol has been updated with new features to improve performance and stability. Some of these new features have a direct impact on the performance of Provisioning Services (PVS) and Machine Creation Services (MCS).

SMB Direct is a new transport protocol which supports network adapters that have Remote Direct Memory Access (RDMA) capability. This enables direct memory-to-memory data transfers between servers, with minimal CPU utilization, and low latency. To Hyper-V 2012 hosts, remote file servers appear as fast as local storage.  By minimizing CPU utilization Hyper-V is able to allocate more CPU cycles to virtual machines and applications.

SMB Multichannel is a new feature that enables bandwidth aggregation through multiple network interfaces.  This improves Machine Creation Services performance when virtual machines are placed on file shares with clustered shared volumes using SMB 3.0.

SMB Transparent Failover is another new feature that enables Windows file shares in a Failover Cluster configuration to be continuously available.  A good example of this would be if a Provisioning Services vDisk is placed on a file share in the cluster.  If a failure occurs on the node, the SMB client on the Provisioning server will reconnect to another file server node in the cluster automatically and Provisioning Services does not experience any downtime.

For a more in depth look at the new SMB 3.0 features please see the Microsoft TechEd 2013 session Understanding the Hyper-V over SMB Scenario, Configurations, and End-to-End Performance presented by Jose Barreto.

3.      Scalability Improvements

Hyper-V 2012 resources scale about 4-16 times higher than Hyper-V 2008 R2.  A Hyper-V 2012 host can support up to 320 logical processors, whereas a Hyper-V 2008 R2 host supports 64. A Hyper-V 2012 host can support up to 4TB of RAM, whereas Hyper-V 2008 R2 supports 1TB.  A Hyper-V 2012 cluster can support up to 64 nodes, which goes well beyond the 16 node limitation of Hyper-V 2008 R2.  For large XenDesktop deployments with adequately sized servers, this will mean fewer hardware resources required in the datacenter to support the environment.  See the chart below from Microsoft’s whitepaper on Windows Server 2012 to see other resource improvements made to Hyper-V 2012.

4.      Live Migration No Longer Restricted to Clusters

In Hyper-V 2008 R2, Live Migration was only possible between nodes in a cluster.  With Hyper-V 2012, it is now possible to “live migrate” between two standalone Hyper-V hosts, or between two stand-alone Hyper-V host clusters.  The file shares in the storage locations must be using SMB 3.0 in order to take advantage of this feature.  This is useful for smaller XenDesktop environments where resources may be limited and dedicating host servers to a cluster may not be feasible, or in test environments where building a cluster is not warranted.

5.      Networking Enhancements

There have been several networking enhancements added in Windows Server 2012 and Hyper-V 2012.

Logical Networks, a new feature in System Center Virtual Machine Manager SP1, allows you to create multiple virtual networks on a physical Hyper-V host for the purpose of isolating network traffic. To accomplish this on Hyper-V 2008 R2 VLANs are typically required. A XenDesktop design may require multiple VLANs to isolate the virtual desktops, the servers supporting the infrastructure, and the traffic from Provisioning Services.  Depending on the use case, using Logical Networks have a distinct advantage over VLANs.  They do not have the design complexity of VLANs.  They do not require a physical switch for traffic isolation, or require the use of VLAN tagging.  VLANs are also restricted to a single IP subnet which usually limits virtual machine creation to a single site.  Logical Networks can be designed to extend across different IP networks. For more information on Logical Networks please see the Microsoft whitepaper on Windows Server 2012.

Virtual Fibre Channel adapter is now supported which makes it possible for virtual machines to access Fibre Channel based storage directly.  This feature is only available for virtual machines running the Windows Server OS (Windows Server 2008, 2008 R2, and 2012).  So while virtual desktops can’t take advantage of this, critical infrastructure servers supporting the XenDesktop environment can. The typical use case where this is valuable is when using Failover Clustering and Live Migration.

NIC Teaming is now native in Windows Server 2012.  While it is possible to team NICs on a Hyper-V 2008 R2 host, it requires the use of third party software and is not supported by Microsoft. The Hyper-V Extensible Switch allows the Hyper-V 2012 host to use the NIC teaming configurations made at the OS level.

Single Route I/O Virtualization (SR-IOV) support is now available.  This allows the functions of the physical network adapter to be available directly to a virtual machine, which increases network throughput and reduces network latency.  This functionality is ideal for virtual Provisioning Services servers. By communicating with the network adapter directly, Provisioning Services is able to perform and scale better.  SR-IOV can also improve the performance of Live Migrations.

6.      Storage Enhancements

Hyper-V 2012 supports 4K sector virtual hard disks which are replacing 512-byte sector disks as the new standard in the storage industry.  Hyper-V 2012 also supports 512 byte sector emulation disks, also referred to as 512e sector disks, which are disks that have a 512-byte logical sector size, but a 4K physical sector size.  This allows support for legacy software written for 512-byte sector disks that are incompatible with 4 KB sector disks. There is a performance hit when using 512e disks due to the “read-modify-write” process involved.

Hyper-V 2012 has a new VHDX format which has increased protection against disk corruption due to power failures.  The VHDX disk has an Intent log which captures all changes to the VHDX metastructure.  If power is lost before changes are written to the disk, the changes are recovered from the Intent log once power is restored.

7.      Provisioning Services 7 can stream over Hyper-V synthetic adapter

One of the limitations when using Provisioning Services 6.x on Hyper-V is that the Hyper-V legacy network adapter is required to boot and stream the vDisk to target devices.  The legacy adapter performs at 100Mbps, so in order to have provisioned VMs use the higher performing synthetic NIC, your option is to assign both the legacy and synthetic network adapters to the virtual machine.  Streaming traffic is bound to the legacy adapter and all other network traffic can run over the synthetic adapter.

Provisioning Services 7 will support streaming traffic over the synthetic NIC in Hyper-V (both 2008 R2 and 2012 versions).  The legacy adapter is still required to boot the virtual machine, approximately the first 20 MB, then after that it will switch over to the synthetic adapter as long as both adapters are on the same subnet.  This feature can be disabled through a registry setting if desired.

8.      Automatic Write Cache & BDM Disks

When using Provisioning Services 7, creating the Write Cache disk is an automated step during the XenDesktop Setup Wizard, as well as the Boot Device Manager (BDM) disk if you prefer to boot the virtual machines without using PXE services. (This feature is also supported in Hyper-V 2008 R2).  You no longer need to build master template images with the write cache disk attached, and using Boot Device Manager has been simplified greatly by removing the manual process involved in configuring the boot partition.

For more information about all the new features in Hyper-V 2012, please visit Microsoft’s What’s New in Microsoft Hyper-V Server 2012. To learn more about XenDesktop 7 on Hyper-V 2012 including information about the architecture, scalability, and tips on improving performance, I encourage you to check out the Microsoft TechEd Europe 2013 sessions presented by my colleague Tony Sanchez. Visit the Citrix website for an evaluation download XenDesktop 7.

Ed Duncan – Senior Consultant
Worldwide Consulting
Desktop & Apps Team
Virtual Desktop Handbook
Project Accelerator