6.0.1

Figure 2‑2. Admission Control Example with Percentage of Cluster Resources Reserved Policy
total resource requirements
7GHz, 6GB
total host resources
24GHz, 21GB
2GHz
1GB
2GHz
1GB
1GHz
2GB
1GHz
1GB
1GHz
1GB
VM1
9GHz
9GB
H1
9GHz
6GB
H2
6GHz
6GB
H3
VM2 VM3 VM4 VM5
The total resource requirements for the powered-on virtual machines is 7GHz and 6GB. The total host
resources available for virtual machines is 24GHz and 21GB. Based on this, the Current CPU Failover
Capacity is 70% ((24GHz - 7GHz)/24GHz). Similarly, the Current Memory Failover Capacity is 71%
((21GB-6GB)/21GB).
Because the cluster's Configured Failover Capacity is set to 25%, 45% of the cluster's total CPU resources and
46% of the cluster's memory resources are still available to power on additional virtual machines.
Specify Failover Hosts Admission Control Policy
You can configure vSphere HA to designate specific hosts as the failover hosts.
With the Specify Failover Hosts admission control policy, when a host fails, vSphere HA attempts to restart
its virtual machines on any of the specified failover hosts. If this is not possible, for example the failover
hosts have failed or have insufficient resources, then vSphere HA attempts to restart those virtual machines
on other hosts in the cluster.
To ensure that spare capacity is available on a failover host, you are prevented from powering on virtual
machines or using vMotion to migrate virtual machines to a failover host. Also, DRS does not use a failover
host for load balancing.
NOTE If you use the Specify Failover Hosts admission control policy and designate multiple failover hosts,
DRS does not attempt to enforce VM-VM affinity rules for virtual machines that are running on failover
hosts.
The Current Failover Hosts appear in the vSphere HA section of the cluster's Summary tab. The status icon
next to each host can be green, yellow, or red.
n
Green. The host is connected, not in maintenance mode, and has no vSphere HA errors. No powered-on
virtual machines reside on the host.
n
Yellow. The host is connected, not in maintenance mode, and has no vSphere HA errors. However,
powered-on virtual machines reside on the host.
n
Red. The host is disconnected, in maintenance mode, or has vSphere HA errors.
vSphere Availability
28 VMware, Inc.