6.5.1

To use the Shutdown and restart VMs seing, you must install VMware Tools in the guest operating system
of the virtual machine. Shuing down the virtual machine provides the advantage of preserving its state.
Shuing down is beer than powering o the virtual machine, which does not ush most recent changes to
disk or commit transactions. Virtual machines that are in the process of shuing down take longer to fail
over while the shutdown completes. Virtual Machines that have not shut down in 300 seconds, or the time
specied in the advanced option das.isolationshutdowntimeout, are powered o.
After you create a vSphere HA cluster, you can override the default cluster seings for Restart Priority and
Isolation Response for specic 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 aempts to
restart the virtual machines that are running on the isolated or partitioned host. This aempt 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 seing, 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 o, leaving
just the instance that has the disk locks.
Virtual Machine Dependencies
You can create dependencies between groups of virtual machines. To do so, you must rst create the VM
groups in the vSphere Web Client by going to the  tab for the cluster and selecting VM/Host
Groups. Once the groups have been created, you can create restart dependency rules between the groups by
browsing toVM/Host Rules and in the Type drop-down menu, select Virtual Machines to Virtual
Machines. These rules can specify that certain VM groups cannot be restarted until other, specied VM
groups have been Ready rst.
Factors Considered for Virtual Machine Restarts
After a failure, the cluster's master host aempts to restart aected virtual machines by identifying a host
that can power them on. When choosing such a host, the master host considers a number of factors.
File accessibility
Before a virtual machine can be started, its les must be accessible from one
of the active cluster hosts that the master can communicate with over the
network
Virtual machine and
host compatibility
If there are accessible hosts, the virtual machine must be compatible with at
least one of them. The compatibility set for a virtual machine includes the
eect of any required VM-Host anity rules. For example, if a rule only
permits a virtual machine to run on two hosts, it is considered for placement
on those two hosts.
Resource reservations
Of the hosts that the virtual machine can run on, at least one must have
sucient unreserved capacity to meet the memory overhead of the virtual
machine and any resource reservations. Four types of reservations are
considered: CPU, Memory, vNIC, and Virtual ash. Also, sucient network
ports must be available to power on the virtual machine.
vSphere Availability
14 VMware, Inc.