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26 End-User Computing For Dummies, Nutanix Special Edition These materials are © 2020 John Wiley & Sons, Inc. Any dissemination, distribution, or unauthorized use is strictly prohibited. Optimizing vCPU:pCPU With server workloads, you have to be careful about oversubscrib- ing physical CPU cores to a point where you have CPU ready/CPU availability concerns. The same holds true in VDI environments. If you add too many virtual CPUs per physical core, your desk- top environment eventually suffers as the host struggles to make physical resources available. In most scenarios, except those in which organizations need to deploy monster desktop virtual machines, you should be able to get a higher vCPU-to-physical CPU (pCPU) ratio than you can with server workloads. General guidance suggests that a 6:1 to 10:1 ratio is safe. You should thus be able to plan on using six to ten virtual CPUs for every core in your system. If you have 500 dual core desktops that have to run concurrently, you need 1,000 cores of capacity. Assuming that each physical processor has ten cores and you have two cores per host, you can support about 100 desktops per host and should plan for about five hosts. Of course, this estimate is general and doesn't consider leaving overhead for spikes and availability. Enabling availability Your VDI environment is likely more critical than many give it credit for and it needs some level of availability. The first step is to design your VDI architecture with an "N+1" mindset. Make sure that it's built so that it can support 100 percent of your desktop environment even if a single host fails. From there, consider the capabilities of the VDI architecture. Hypervisors often have built-in availability mechanisms that can be leveraged by the VDI deployment. For example, if you're using VMware Horizon, you can use vSphere's high-availability feature to ensure automatic failover for particularly critical desktops. In some environments, failure is truly not an option. Consider healthcare. In such environments, look for additional availability guidance from your VDI vendor. For example, VMware Horizon provides what the company calls an AlwaysOn architecture for these types of environments and makes available comprehensive guidance for all aspects of the environment.