6.0.1

n
Medium. Application servers that consume data in the database and provide results on web pages.
n
Low. Web servers that receive user requests, pass queries to application servers, and return results to
users.
If a host fails, vSphere HA attempts to register to an active host the affected virtual machines that were
powered on and have a restart priority setting of Disabled, or that were powered off.
Host Isolation Response
Host isolation response determines what happens when a host in a vSphere HA cluster loses its
management network connections, but continues to run. You can use the isolation response to have vSphere
HA power off virtual machines that are running on an isolated host and restart them on a nonisolated host.
Host isolation responses require that Host Monitoring Status is enabled. If Host Monitoring Status is
disabled, host isolation responses are also suspended. A host determines that it is isolated when it is unable
to communicate with the agents running on the other hosts, and it is unable to ping its isolation addresses.
The host then executes its isolation response. The responses are Power off and restart VMs or Shutdown and
restart VMs. You can customize this property for individual virtual machines.
NOTE If a virtual machine has a restart priority setting of Disabled, no host isolation response is made.
To use the Shutdown and restart VMs setting, you must install VMware Tools in the guest operating system
of the virtual machine. Shutting down the virtual machine provides the advantage of preserving its state.
Shutting down is better than powering off the virtual machine, which does not flush most recent changes to
disk or commit transactions. Virtual machines that are in the process of shutting down take longer to fail
over while the shutdown completes. Virtual Machines that have not shut down in 300 seconds, or the time
specified in the advanced option das.isolationshutdowntimeout, are powered off.
After you create a vSphere HA cluster, you can override the default cluster settings for Restart Priority and
Isolation Response for specific virtual machines. Such overrides are useful for virtual machines that are used
for special tasks. For example, virtual machines that provide infrastructure services like DNS or DHCP
might need to be powered on before other virtual machines in the cluster.
A virtual machine "split-brain" condition can occur when a host becomes isolated or partitioned from a
master host and the master host cannot communicate with it using heartbeat datastores. In this situation, the
master host cannot determine that the host is alive and so declares it dead. The master host then attempts to
restart the virtual machines that are running on the isolated or partitioned host. This attempt succeeds if the
virtual machines remain running on the isolated/partitioned host and that host lost access to the virtual
machines' datastores when it became isolated or partitioned. A split-brain condition then exists because
there are two instances of the virtual machine. However, only one instance is able to read or write the
virtual machine's virtual disks. VM Component Protection can be used to prevent this split-brain condition.
When you enable VMCP with the aggressive setting, it monitors the datastore accessibility of powered-on
virtual machines, and shuts down those that lose access to their datastores.
To recover from this situation, ESXi generates a question on the virtual machine that has lost the disk locks
for when the host comes out of isolation and cannot reacquire the disk locks. vSphere HA automatically
answers this question, allowing the virtual machine instance that has lost the disk locks to power off,
leaving just the instance that has the disk locks.
vSphere Availability
16 VMware, Inc.