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Figure 6:
VDI consolidation is heavily driven by the ratio of vCPU your virtual desktops will be
configured with. The chart represents a range that experience has proven to be safe.
The working range to operate normally for single vCPU virtual desktops is between 8:1
and 20:1. This is a large range, and where one would land in that range is driven by
different choices. One would be how large the hosts are, the number of VMs per host,
and the customer's comfort level with that number. An example would be a dual socket
host with dual 18 core CPUs. This could accommodate upwards of 700+ VMs on the
high side, providing you have the right amount of memory and enough clock speed
available. Typically, having that many VMs on a single host would scare most customers.
Consequently, there are two choices to make in this scenario, first is to choose a lower
density that one is artificially limiting. If one chooses the lower end of the ratio, it would
net 288 VMs on the same host. The second option would be to choose CPUs with fewer
cores, but choose a ratio somewhere in the middle. If one chooses 12 core CPUs and
uses a 12:1 ratio, that would net 288 VMs. This decision is typically a combination of
customer feedback, architect's recommendations, and infrastructure pricing. There
may be significant cost savings from choosing different physical CPU configurations.
The calculations for a dual vCPU virtual desktop are similar, except that one is now
dealing with double the amount of vCPUs. The range to operate here is between 4:1
and 8:1. Some vendors promise higher, but these recommendations are driven by
real customer deployments. One should use the same decision points as the previous
example, just with a different CPU ratio range.
1 vCPU VM
2 vCPU VM
8:1 20:1
4:1 8:1
