Performance

Without actual performance metrics, it will be near on impossible to size your virtual desktops. If you don't have this data, then it will be likely that your desktops will be sized in one of two ways. The first would be by oversizing your desktops. Oversizing often occurs when virtualizing as it is so simple to configure a virtual machine that we sometimes get carried away and start adding more CPU and memory than we really need. The result is that we need more infrastructure to resource this and so the costs goes up. This also happens when we guesstimate the size of the desktop, and then add ten or twenty percent on top of that, just in case. Pushing the costs up could mean that the project is not financially viable.

The flipside would be to undersize your desktops, potentially causing performance issues and a poor end user experience. If you then base your infrastructure on this lower spec and you end up having to add more resources, it may be a difficult conversation to secure more budget to increase the spec of the host servers or even add more servers.

This is one to watch out for if you are looking at a Desktop as a Service solution. On paper, the desktops look like they're good value for money, maybe costing somewhere around $30 to $50 per month. But after you have signed on the dotted line and your end users start ramping up and consuming more resources, the costs start to ramp up too. We have seen many a customer invoice with a much larger monthly payment than budgeted for because of taking low-spec desktops.

By performing a desktop assessment, you will understand what the performance looks like throughout the working day. How many resources are being consumed, and when? You are likely to see many dips and spikes throughout the day, such as login storms, AV scans, logoff storms, and other metrics, such as increased internet usage during lunch breaks.

If you work in an education environment, you might see many login and logoff storms during the day. It is important to understand this, as you will need to ensure that your solution is designed to meet these requirements. This information can be used to help guide you when sizing the relevant desktop pools, but bear in mind that, potentially, you are going to be making changes to the desktops between the assessment phase and deploying VDI desktops. This may be something such as migrating from Windows 7 to Windows 10, or the upgrade of an application. In these cases, the assessment will have been performed on the previous version of the operating system and therefore may not give you 100% accurate information on the resources required. Some third-party assessment tools can take care of this and allow you to model "what if" type scenarios.