Users Guide

Introduction to the VMware Virtual Infrastructure 29
VMware Virtual Infrastructure Overview
Datastores are host-independent and platform-independent. Therefore, they do not
change in any way when the virtual machines contained within them are moved from
one ESX Server to another.
Clusters
A Cluster object is a group of VMware ESX Servers that share common storage
resources and network configurations. A Cluster represents a pool of the combined
resources of all of the ESX Server Hosts assigned to the Cluster. For example, if four
ESX Servers are added to a Cluster and each ESX Server has 2x2 GHz processors with
4 GB of memory, the Cluster represents a pool of 16 GHz of CPU processing power and
16 GB of memory that is available for use by virtual machines.
A Cluster also serves as the boundary for virtual machine migration activity through the
VMware VMotion or VMware HA features. When using either of these technologies for
virtual machine migration it is critical that the participating ESX Server Hosts have
identical storage resource and network configurations, and this is guaranteed within a
Cluster by the very definition of a Cluster.
Resource Pools
Resource Pools enable an administrator to fine tune resource allocations within a
Cluster. A Resource Pool can be configured to leverage a portion of the overall available
resources within a Cluster and then virtual machines can be assigned to that Resource
Pool. This enables an administrator to prioritize virtual machines—to either limit or
guarantee certain resources to a particular virtual machine or group of virtual machines.
Resource Pools can be configured in many ways, from simple to complex. For a simple
example, two Resource Pools are configured within a Cluster; one is named Production
Virtual Machines and the other is named Development Virtual machines. The
Production Resource Pool is configured with a "High" share priority and the
Development Resource Pool is configured with the default "Normal" share priority. In
this case any virtual machine residing in the Production Resource Pool is automatically
given twice the priority, in terms of access to system resources during periods of
contention, of any virtual machine residing in the Development Resource Pool.
To better demonstrates the true potential of using Resource Pools, the following is an
advanced example. Four ESX Servers are added to a Cluster and each ESX Server has
2x2 GHz processors with 4 GB of memory. The Cluster therefore represents a pool of
16 GHz of CPU processing power and 16 GB of memory that is available for use by
virtual machines. Figure 2 below illustrates that the Production Cluster resource that
resides in the Chicago Datacenter has 16 GHz of processing power and 16 GB of
memory. A Resource Pool is created for a CRM Application that has access to 8 GHz of