This content is part of the Essential Guide: What you need to know about application performance monitoring tools

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Testing VDI network performance to avoid application meltdown

Ensuring VDI network performance is central to providing a good VDI user experience, so engineers must start by testing the impact of VDI on bandwidth and traffic flow.

If left unchecked, Virtual Desktop Infrastructure (VDI) can place a major strain on your network, directly impacting application performance and the end user experience in the process. But how do you know if your network is delivering the bandwidth that your VDI needs? There are numerous techniques for quantifying VDI network performance to ensure applications performance.

VDI application performance: Benchmarking the end user experience

Regardless of the statistics that your benchmarking software might provide, the most important aspect of overall performance is the end user experience. End users do not care that you have implemented a cool new VDI system, they just expect the system to work as well or better than it has in the past.

If the network is saturated with traffic, or if the backend VDI servers are overloaded, applications will perform poorly and the end user experience will be less than desirable. In extreme cases users might even see a delay of a second or two between the time they press a key and the time the letter or number that they pressed shows up on the screen.

As such, one of the best ways to quantify the end user experience is to compare application load times in your VDI environment against that of a standalone PC. For example, you might compare the amount of time that it takes Microsoft Word to load in each environment. Users probably won’t notice a difference of a few seconds, but if there is a difference of more than five seconds, you will have to take steps to improve your infrastructure’s performance.

You can also test the end user experience by examining computationally intensive tasks. For example, if the finance department regularly runs a complex report, you could compare the amount of time it takes to run the report on a virtual desktop against the amount of time that it takes to run the same report on a standard PC.

Regardless of how you decide to benchmark the end user experience, it is important to consider the impact of network load and timing. Running a set of benchmark tests at 9:00 a.m. when everyone is logging on for the day is almost certain to yield different performance data than if you run the same tests late at night. You will, of course, get the most accurate test results by performing your benchmark tests while the VDI network is experiencing its heaviest workloads.

Another way to quantify your VDI performance is by using a free tool called Login VSI. This tool not only lets you benchmark your VDI deployment, but it also enables you to test the effects of any modifications that you make along the way.

VDI network problems: Seeking signs of saturation

VDI environments generate a greater volume of network traffic than non-VDI environments. But some VDI-related protocols are more efficient than others, so it is important to examine your network for signs of saturation.

There are many ways to test for network saturation, but the method that is most appropriate will vary depending on each organization's infrastructure. Ping testing on network interfaces at VDI servers is one of the simpler tests. Although Ping has traditionally been used to look for packet loss, the utility also reports response time. This information could be useful in network latency testing. Tracert can be used in a similar manner.

If your VDI servers are Windows based, you can use Performance Monitor to collect information about inbound and outbound traffic on each network interface. If you use this method, however, there are two things that you must keep in mind. First, the number of packets sent and received is irrelevant because packet sizes are not always consistent. What you should be looking for is the number of bytes sent and received. Second, you need to remember that performance monitoring can have a negative impact on system performance if you sample data too frequently.

Using SNMP is another option for testing network saturation. Many network switches have built in SNMP monitoring capabilities that let you see if the network is performing well.

Regardless of which method you use to check for network saturation, there are multiple network paths that need to be analyzed. You will want to check the path between the VDI clients and the VDI front-end servers (typically the load balancers). You will also want to check the links between the VDI front-end and the VDI back-end. Depending on how your VDI infrastructure is set up, this might be a multi-step process. Finally, you will need to check the links between your host servers and your storage architecture.

Depending on the type of problem you find, you might try prioritizing network traffic or scaling out network load balancing. You might also benefit from faster network connections between VDI servers and to your storage infrastructure.

Read part two of this series on VDI networking, which focuses on converged storage networking for virtual desktop environments.

About the author:
Brien M. Posey, MCSE, is a Microsoft Most Valuable Professional for his work with Windows 2000 Server and IIS. He has served as CIO for a nationwide chain of hospitals and was once in charge of IT security for Fort Knox. As a freelance technical writer, he has written for Microsoft, TechTarget, CNET, ZDNet, MSD2D, Relevant Technologies and other technology companies.

This was last published in January 2012

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