1. The Host Failures Cluster Tolerates admission control policy is based on the calculation on a slot size comprised of two components, the CPU and memory reservations of a virtual machine.
2. A slot represents the minimum CPU and memory resources that are required to support any powered-on virtual machine in the cluster. With the failover level policy in place, HA uses the following slot calculations to control virtual machine migration within the cluster: Calculate the slot size from CPU and memory reservations.
3. You can also have option to choose “Slot Policy”. This is the default option prior to vSphere 6.5. Slot Size is defined as the memory and CPU resources that satisfy the reservation requirements for any powered-on virtual machines in the HA cluster. Take a look how HA slot Size is calculated. You have 2 options under Slot.
4. VMware's lifecycle policy matrix is based on enterprise industry standards and details the level of support you can expect as your VMware purchase matures. Consult or download the Lifecycle Policy Matrix below frequently to be sure you have the most up to date information.

1. Vmware Slot Size Policy Guide
2. Vmware Slot Size Policy Chart
3. Vmware Slot Size Policy Comparison
4. Vmware Slot Size Policy Tool

After you create a cluster, you can configure admission control to specify whether virtual machines can be started if they violate availability constraints. The cluster reserves resources so that failover can occur for all running virtual machines on the specified number of hosts.

Vmware Slot Size Policy Guide

The Admission Control page appears only if you enabled vSphere HA.

Vmware Slot Size Policy Chart

Procedure

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Vmware Slot Size Policy Comparison

1. In the vSphere Client, browse to the vSphere HA cluster.
2. Click the Configure tab.
3. Select vSphere Availability and click Edit.
4. Click Admission Control to display the configuration options.
5. Select a number for the Host failures cluster tolerates. This is the maximum number of host failures that the cluster can recover from or guarantees failover for.
6. Select an option for Define host failover capacity by. Option

   Description
   Cluster resource percentage	Specify a percentage of the cluster’s CPU and memory resources to reserve as spare capacity to support failovers.
   Slot Policy (powered-on VMs)	Select a slot size policy that covers all powered on VMs or is a fixed size. You can also calculate how many VMs require multiple slots.
   Dedicated failover hosts	Select hosts to use for failover actions. Failovers can still occur on other hosts in the cluster if a default failover host does not have enough resources.
   Disabled	Select this option to disable admission control and allow virtual machine power ons that violate availability constraints.

7. Set the percentage for the Performance degradation VMs tolerate.
   This setting determines what percentage of performance degradation the VMs in the cluster are allowed to tolerate during a failure.
8. Click OK.

Vmware Slot Size Policy Tool

Your admission control settings take effect.