6.5.1
Table Of Contents
- vSphere Availability
- Contents
- About vSphere Availability
- Business Continuity and Minimizing Downtime
- Creating and Using vSphere HA Clusters
- Providing Fault Tolerance for Virtual Machines
- vCenter High Availability
- Plan the vCenter HA Deployment
- Configure the Network
- Configure vCenter HA With the Basic Option
- Configure vCenter HA With the Advanced Option
- Manage the vCenter HA Configuration
- Set Up SNMP Traps
- Set Up Your Environment to Use Custom Certificates
- Manage vCenter HA SSH Keys
- Initiate a vCenter HA Failover
- Edit the vCenter HA Cluster Configuration
- Perform Backup and Restore Operations
- Remove a vCenter HA Configuration
- Reboot All vCenter HA Nodes
- Change the Appliance Environment
- Collecting Support Bundles for a vCenter HA Node
- Troubleshoot Your vCenter HA Environment
- Patching a vCenter High Availability Environment
- Using Microsoft Clustering Service for vCenter Server on Windows High Availability
- Index
vSphere HA Admission Control
vSphere HA uses admission control to ensure that sucient resources are reserved for virtual machine
recovery when a host fails.
Admission control imposes constraints on resource usage. Any action that might violate these constraints is
not permied. Actions that might be disallowed include the following examples:
n
Powering on a virtual machine
n
Migrating a virtual machine
n
Increasing the CPU or memory reservation of a virtual machine
The basis for vSphere HA admission control is how many host failures your cluster is allowed to tolerate
and still guarantee failover. The host failover capacity can be set in three ways:
n
Cluster resource percentage
n
Slot policy
n
Dedicated failover hosts
N vSphere HA admission control can be disabled. However, without it you have no assurance that the
expected number of virtual machines can be restarted after a failure. Do not permanently disable admission
control.
Regardless of the admission control option chosen, a VM resource reduction threshold also exists. You use
this seing to specify the percentage of resource degradation to tolerate, but it is not available unless
vSphere DRS is enabled.
The resource reduction calculation is checked for both CPU and memory. It considers a virtual machine's
reserved memory and memory overload to decide whether to permit it to power on, migrate, or have
reservation changes. The actual memory consumed by the virtual machine is not considered in the
calculation because the memory reservation does not always correlate with the actual memory usage of the
virtual machine. If the actual usage is more than reserved memory, insucient failover capacity is available,
resulting in performance degradation on failover.
Seing a performance reduction threshold enables you to specify the occurrence of a conguration issue. For
example:
n
The default value is 100%, which produces no warnings.
n
If you reduce the threshold to 0%, a warning is generated when cluster usage exceeds the available
capacity.
n
If you reduce the threshold to 20%, the performance reduction that can be tolerated is calculated as
performance reduction = current utilization * 20%. When the current usage minus the performance
reduction exceeds the available capacity, a conguration notice is issued.
Cluster Resources Percentage Admission Control
You can congure vSphere HA to perform admission control by reserving a specic percentage of cluster
CPU and memory resources for recovery from host failures.
With this type of admission control, vSphere HA ensures that a specied percentage of aggregate CPU and
memory resources are reserved for failover.
With the cluster resources percentage option, vSphere HA enforces admission control as follows:
1 Calculates the total resource requirements for all powered-on virtual machines in the cluster.
2 Calculates the total host resources available for virtual machines.
Chapter 2 Creating and Using vSphere HA Clusters
VMware, Inc. 19