Performance Tuning Remote Desktop Virtualization Hosts

Remote Desktop Virtualization Host (RD Virtualization Host) is a role service that supports Virtual Desktop Infrastructure (VDI) scenarios and lets multiple users run Windows-based applications in virtual machines hosted on a server running Windows Server and Hyper-V.

Windows Server supports two types of virtual desktops: personal virtual desktops and pooled virtual desktops.

General considerations

Storage

Storage is the most likely performance bottleneck, and it is important to size your storage to properly handle the I/O load that is generated by virtual machine state changes. If a pilot or simulation is not feasible, a good guideline is to provision one disk spindle for four active virtual machines. Use disk configurations that have good write performance (such as RAID 1+0).

When appropriate, use Disk Deduplication and caching to reduce the disk read load and to enable your storage solution to speed up performance by caching a significant portion of the image.

Data Deduplication and VDI

Introduced in Windows Server 2012 R2, Data Deduplication supports optimization of open files. In order to use virtual machines running on a deduplicated volume, the virtual machine files need to be stored on a separate host from the Hyper-V host. If Hyper-V and deduplication are running on the same machine, the two features will contend for system resources and negatively impact overall performance.

The volume must also be configured to use the "Virtual Desktop Infrastructure (VDI)" deduplication optimization type. You can configure this by using Server Manager (File and Storage Services -> Volumes -> Dedup Settings) or by using the following Windows PowerShell command:

Enable-DedupVolume <volume> -UsageType HyperV

Note

Data Deduplication optimization of open files is supported only for VDI scenarios with Hyper-V using remote storage over SMB 3.0.

Memory

Server memory usage is driven by three main factors:

• Operating system overhead

• Hyper-V service overhead per virtual machine

• Memory allocated to each virtual machine

For a typical knowledge worker workload, guest virtual machines running x86 Window 8 or Windows 8.1 should be given ~512 MB of memory as the baseline. However, Dynamic Memory will likely increase the guest virtual machine's memory to about 800 MB, depending on the workload. For x64, we see about 800 MB starting, increasing to 1024 MB.

Therefore, it is important to provide enough server memory to satisfy the memory that is required by the expected number of guest virtual machines, plus allow a sufficient amount of memory for the server.

CPU

When you plan server capacity for an RD Virtualization Host server, the number of virtual machines per physical core will depend on the nature of the workload. As a starting point, it is reasonable to plan 12 virtual machines per physical core, and then run the appropriate scenarios to validate performance and density. Higher density may be achievable depending on the specifics of the workload.

We recommend enabling hyper-threading, but be sure to calculate the oversubscription ratio based on the number of physical cores and not the number of logical processors. This ensures the expected level of performance on a per CPU basis.

Performance optimizations

Dynamic Memory

Dynamic Memory enables more efficiently utilization of the memory resources of the server running Hyper-V by balancing how memory is distributed between running virtual machines. Memory can be dynamically reallocated between virtual machines in response to their changing workloads.

Dynamic Memory enables you to increase virtual machine density with the resources you already have without sacrificing performance or scalability. The result is more efficient use of expensive server hardware resources, which can translate into easier management and lower costs.

On guest operating systems running Windows 8 and above with virtual processors that span multiple logical processors, consider the tradeoff between running with Dynamic Memory to help minimize memory usage and disabling Dynamic Memory to improve the performance of an application that is computer-topology aware. Such an application can leverage the topology information to make scheduling and memory allocation decisions.

Tiered Storage

RD Virtualization Host supports tiered storage for virtual desktop pools. The physical computer that is shared by all pooled virtual desktops within a collection can use a small-size, high-performance storage solution, such as a mirrored solid-state drive (SSD). The pooled virtual desktops can be placed on less expensive, traditional storage such as RAID 1+0.

The physical computer should be placed on a SSD is because most of the read-I/Os from pooled virtual desktops go to the management operating system. Therefore, the storage that is used by the physical computer must sustain much higher read I/Os per second.

This deployment configuration assures cost effective performance where performance is needed. The SSD provides higher performance on a smaller size disk (~20 GB per collection, depending on the configuration). Traditional storage for pooled virtual desktops (RAID 1+0) uses about 3 GB per virtual machine.

CSV cache

Failover Clustering in Windows Server 2012 and above provides caching on Cluster Shared Volumes (CSV). This is extremely beneficial for pooled virtual desktop collections where the majority of the read I/Os come from the management operating system. The CSV cache provides higher performance by several orders of magnitude because it caches blocks that are read more than once and delivers them from system memory, which reduces the I/O. For more info on CSV cache, see How to Enable CSV Cache.

Pooled virtual desktops

By default, pooled virtual desktops are rolled back to the pristine state after a user signs out, so any changes made to the Windows operating system since the last user sign-in are abandoned.

Although it's possible to disable the rollback, it is still a temporary condition because typically a pooled virtual desktop collection is re-created due to various updates to the virtual desktop template.

It makes sense to turn off Windows features and services that depend on persistent state. Additionally, it makes sense to turn off services that are primarily for non-enterprise scenarios.

Each specific service should be evaluated appropriately prior to any broad deployment. The following are some initial things to consider:

Service	Why?
Auto update	Pooled virtual desktops are updated by re-creating the virtual desktop template.
Offline files	Virtual desktops are always online and connected from a networking point-of-view.
Background defrag	File-system changes are discarded after a user signs off (due to a rollback to the pristine state or re-creating the virtual desktop template, which results in re-creating all pooled virtual desktops).
Hibernate or sleep	No such concept for VDI
Bug check memory dump	No such concept for pooled virtual desktops. A bug-check pooled virtual desktop will start from the pristine state.
WLAN autoconfig	There is no WiFi device interface for VDI
Windows Media Player network sharing service	Consumer centric service
Home group provider	Consumer centric service
Internet connection sharing	Consumer centric service
Media Center extended services	Consumer centric service

Note

This list is not meant to be a complete list, because any changes will affect the intended goals and scenarios. For more info, see Hot off the presses, get it now, the Windows 8 VDI optimization script, courtesy of PFE!.

Note

SuperFetch in Windows 8 is enabled by default. It is VDI-aware and should not be disabled. SuperFetch can further reduce memory consumption through memory page sharing, which is beneficial for VDI. Pooled virtual desktops running Windows 7, SuperFetch should be disabled, but for personal virtual desktops running Windows 7, it should be left on.