Information Technology Reference
In-Depth Information
Now that we've covered OS clustering in Windows Server, let's take a look at VMware's ver-
sion of high availability. VMware has a built-in option called vSphere High Availability (HA).
As you'll see, vSphere HA uses a very different method than OS clustering to provide high
availability.
Implementing vSphere High Availability
You've already seen how you can use OS clustering to provide high availability for OSes and
applications. In addition to OS clustering, vSphere provides a feature intended to provide high
availability at the virtualization layer. vSphere High Availability (HA) is a component of the
vSphere product that provides for the automatic failover of VMs. Because the term
high
avail-
ability
can mean different things to different people, it's important to understand the behavior
of vSphere HA to ensure that you are using the right high-availability mechanism to meet the
requirements of your organization. Depending on your requirements, one of the other high-
availability mechanisms described in this chapter might be more appropriate.
A Complete Rewrite from Previous Versions
h e underpinnings of vSphere HA underwent a complete rewrite for vSphere 5.0. If you are familiar
with older versions of vSphere, keep this in mind as you look at how vSphere HA behaves in this
version.
Understanding vSphere High Availability
The vSphere HA feature is designed to provide an automatic restart of the VMs that were run-
ning on an ESXi host at the time it became unavailable, as shown in Figure 7.12.
Figure 7.12
vSphere HA pro-
vides an automatic
restart of VMs that
were running on an
ESXi host when it
failed.
ESXi host
ESXi host
