6.0.1

n
T=320s: vSphere HA now starts the APD recovery response after the Delay for VM failover for APD
elapses (3 minutes after the APD Timeout is reached).
Network Partitions
When a management network failure occurs for a vSphere HA cluster, a subset of the cluster's hosts might
be unable to communicate over the management network with the other hosts. Multiple partitions can occur
in a cluster.
A partitioned cluster leads to degraded virtual machine protection and cluster management functionality.
Correct the partitioned cluster as soon as possible.
n
Virtual machine protection. vCenter Server allows a virtual machine to be powered on, but it can be
protected only if it is running in the same partition as the master host that is responsible for it. The
master host must be communicating with vCenter Server. A master host is responsible for a virtual
machine if it has exclusively locked a system-defined file on the datastore that contains the virtual
machine's configuration file.
n
Cluster management. vCenter Server can communicate with the master host, but only a subset of the
slave hosts. As a result, changes in configuration that affect vSphere HA might not take effect until after
the partition is resolved. This failure could result in one of the partitions operating under the old
configuration, while another uses the new settings.
Datastore Heartbeating
When the master host in a vSphere HA cluster can not communicate with a slave host over the management
network, the master host uses datastore heartbeating to determine whether the slave host has failed, is in a
network partition, or is network isolated. If the slave host has stopped datastore heartbeating, it is
considered to have failed and its virtual machines are restarted elsewhere.
vCenter Server selects a preferred set of datastores for heartbeating. This selection is made to maximize the
number of hosts that have access to a heartbeating datastore and minimize the likelihood that the datastores
are backed by the same LUN or NFS server.
You can use the advanced option das.heartbeatdsperhost to change the number of heartbeat datastores
selected by vCenter Server for each host. The default is two and the maximum valid value is five.
vSphere HA creates a directory at the root of each datastore that is used for both datastore heartbeating and
for persisting the set of protected virtual machines. The name of the directory is .vSphere-HA. Do not delete
or modify the files stored in this directory, because this can have an impact on operations. Because more
than one cluster might use a datastore, subdirectories for this directory are created for each cluster. Root
owns these directories and files and only root can read and write to them. The disk space used by vSphere
HA depends on several factors including which VMFS version is in use and the number of hosts that use the
datastore for heartbeating. With vmfs3, the maximum usage is approximately 2GB and the typical usage is
approximately 3MB. With vmfs5 the maximum and typical usage is approximately 3MB. vSphere HA use of
the datastores adds negligible overhead and has no performance impact on other datastore operations.
vSphere HA limits the number of virtual machines that can have configuration files on a single datastore.
See Configuration Maximums for updated limits. If you place more than this number of virtual machines on a
datastore and power them on, vSphere HA protects a number of virtual machines only up to the limit.
NOTE A Virtual SAN datastore cannot be used for datastore heartbeating. Therefore, if no other shared
storage is accessible to all hosts in the cluster, there can be no heartbeat datastores in use. However, if you
have storage that can be reached by an alternate network path that is independent of the Virtual SAN
network, you can use it to set up a heartbeat datastore.
Chapter 2 Creating and Using vSphere HA Clusters
VMware, Inc. 21