Information Technology Reference
In-Depth Information
Figure 1.3
h e vSphere HA
feature will restart
any VMs that were
previously running
on an ESXi host
that experiences
server failure.
ESXi host
ESXi host
The vSphere HA feature, unlike DRS, does not use the vMotion technology as a means of
migrating servers to another host. vMotion applies only to planned migrations, where both
the source and destination ESXi host are running and functioning properly. In a vSphere
HA failover situation, there is no anticipation of failure; it is not a planned outage, and there-
fore there is no time to perform a vMotion operation. vSphere HA is intended to minimize
unplanned downtime because of the failure of a physical ESXi host or other infrastructure
components. We'll go into more detail in Chapter 7 on what kinds of failures vSphere HA helps
protect against.
vSphere HA Improvements in vSphere
vSphere HA received a couple of notable improvements in the vSphere 5.0 release. First, scalability
was signifi cantly improved; you could run up to 512 VMs per host (up from 100 in earlier versions)
and 3,000 VMs per cluster (up from 1,280 in earlier versions). Second, vSphere HA integrated more
closely with the intelligent placement functionality of vSphere DRS, giving vSphere HA greater
ability to restart VMs in the event of a host failure. h e third and perhaps most signifi cant improve-
ment is the complete rewrite of the underlying architecture for vSphere HA; this entirely new
architecture, known as Fault Domain Manager (FDM), eliminated many of the constraints found
in earlier versions of VMware vSphere.
By default, vSphere HA does not provide failover in the event of a guest OS failure, although
you can coni gure vSphere HA to monitor VMs and restart them automatically if they fail to
respond to an internal heartbeat. This feature is called VM Failure Monitoring, and it uses a
combination of internal heartbeats and I/O activity to attempt to detect if the guest OS inside a
VM has stopped functioning. If the guest OS has stopped functioning, the VM can be restarted
automatically.
