Information Technology Reference
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by the development VMs (VMs found in the DevelopmentVMs resource pool). In this example,
you used all three values—Shares, Reservation, and Limit—in an effort to accomplish your goal.
Let's look at the behavior of each of these values when used on a resource pool.
Managing CPU Usage with Resource Pools
First we'll examine the Shares value assigned to the resource pools for CPU usage. As you can
see in Figure 11.10, the CPU shares for the ProductionVMs resource pool are set to High (8,000).
Figure 11.11 shows the DevelopmentVMs CPU shares set to Low (2,000). The effect of these
two settings is similar to that of comparing two VMs' Shares values for CPU—except in this
case, if there is any competition for CPU resources between VMs in the ProductionVMs and
DevelopmentVMs resource pools, the entire ProductionVMs resource pool and all the VMs in
it would have higher priority. Figure 11.13 shows how this would break down with two VMs in
each resource pool.
Figure 11.13
Two resource
pools with diff er-
ent Shares values
will be allocated
resources pro-
portional to their
percentage of share
ownership.
ESXi Host
ProductionVMs
resource pool
8,000 of 10,000 shares
assigned at this level;
equates to 80%
of host CPU
DevelopmentVMs
resource pool
2,000 of 10,000 shares
assigned at this level;
equates to 20%
of host CPU
As you consider the information presented in Figure 11.13, keep in mind that the resource
allocation occurs at each level. There are only two resource pools under the given ESXi host, so
the CPU is allocated 80/20 according to its Shares value. This means that the ProductionVMs
resource pool gets 80 percent of the CPU time while the DevelopmentVMs resource pool gets
only 20 percent of the CPU time.
Now let's expand on Figure 11.13 and add the two VMs in each resource pool to get a more
complete view of how Shares values would work with a resource pool. Within the resource pool
the CPU Shares values assigned to the VMs, if any at all, come into play. Figure 11.14 shows how
this works.
In Figure 11.14, there are no custom CPU shares assigned to the VMs, so they all use the
default value of 1,000 CPU shares. With two VMs in the resource pool, this means each VM gets
50 percent of the resources available to the resource pool in which it is located (because each
VM has 50 percent of the total number of shares assigned within the pool). In this example, this
means 40 percent of the host CPU capacity will go to each of the two VMs in the ProductionVMs
resource pool. If there were three VMs in each resource pool, then the CPU allocated to the
parent resource pool would be split three ways. Similarly, if there were four VMs, then the
CPU would be split four ways. You can verify this breakdown of resource allocation using the
Monitor tab on the selected cluster, ESXi host, or resource pool. Figure 11.15 shows the Resource
