Users Guide

Clustering Implementations for High Availability 13
require clustering capabilities in the guest operating systems in the VMs. The
only requirement is that all the virtual machine files are on storage accessible
by all the physical servers that are part of the cluster. In this document, we
will refer to VMs managed by the cluster for high availability as "HA VMs".
Hyper-V Host Clustering is the recommended mechanism to implement HA
in a Hyper-V environment. It has many advantages including a wide array of
configuration options, ease of management, and scalability. In addition to
providing HA, this solution also supports planned downtime activities such as
for physical server maintenance and enabling dynamic datacenter capabilities
such as VM workload balancing.
Windows Server 2008 supports a maximum of 16 physical servers in a single
Failover Cluster configuration. Therefore a single Hyper-V Host Cluster
configuration can have a maximum of 16 physical servers. Hyper-V Host
Clustering may be implemented on the following editions of Windows
Server 2008:
• Windows Server 2008 x64 Enterprise Edition
• Windows Server 2008 x64 Datacenter Edition
Planned and Unplanned Failover (Host Cluster
Model Only)
The Hyper-V Host Cluster model accommodates both planned and
unplanned downtime. A planned downtime is when a physical server that is
part of a Hyper-V Host Cluster is taken offline by the administrator for
maintenance such as a hardware upgrade or applying an OS patch. An
unplanned downtime is when a physical server that is part of a Hyper-V Host
Cluster becomes offline unexpectedly due to hardware failure, a parent
partition crash, or other reason. Physical servers that are part of a cluster are
commonly referred to as "cluster nodes".