You can deploy ArcGIS Server in a virtualized environment, such as VMware vSphere. When setting up your site in a virtualized hardware infrastructure, there are some best practices to follow in order to optimize stability and performance.
Leave hardware resources for the hypervisor
Ensure that enough resources are available or directly assigned to the host hypervisor. This includes CPU and memory resources. If you need specific guidance on how many resources to leave available and how to assign those resources, consult the product documentation for the hypervisor provider.
Be aware of disk I/O
ArcGIS Server can be very disk intensive, especially for operations such as serving tiles for cached map services or reading data from local data sources such as a file geodatabase. Ensure that individual virtual machines do not run on the same single physical disk. If possible, use high-performance solid state drives (SSDs).
Use a single virtual network
VMware and other virtualization technologies allow the creation of multiple virtualized network segments. However, ArcGIS Server components should always be installed and run within a single virtual network to avoid disrupting communications.
CPU recommendations
It's recommended that you use a few large virtual machines as opposed to many small virtual machines. For example, a single virtual machine with eight CPUs will perform better than four virtual machines each with two CPUs. If you're configuring failover, high availability, or separate ArcGIS Server sites for separate purposes, follow the recommendation above to determine the size of machines in each site.