7.5 Dedicated Island Clusters
The concept of island clusters is straightforward. An island cluster hosts workloads with special license requirements and is sometimes also referred to as a “dedicated application cluster.” Some software vendors apply special licensing policies on their applications, middleware, or databases that are not conducive to virtualization or hosted cloud environments, especially where vSphere DRS is employed and the application could potentially touch a high number of physical CPUs. Island clusters is one approach of dealing with this challenge.
Use cases for island clusters might include:
• Running Oracle databases, middleware, or applications on dedicated clusters will not only provide that you are able to consolidate more and more Oracle virtual machines on a small cluster of ESXi hosts, but also reduce licensing costs by limiting the number of physical CPUs that require licensing (if this is your Oracle licensing model).
• Customers, particularly service providers, also use island clusters of operating systems such as Windows or RHEL. This helps you save money on data center Windows OS socket licenses, which is typically the most cost efficient way of licensing large numbers of Windows virtual machines running on a host. Another side benefit of this approach is that it helps ESXi to take advantage of the memory management technique of Transparent Page Sharing (TPS), if enabled. This is more efficient because there are higher chances that when you are running many of the same operating system virtual machines, duplicate pages will be spawned by these VMs in physical memory, making your ESXi servers more efficient.
Figure 22. Island Clusters
In addition, service providers can back this strategy with automation, ensuring that specific operating system templates are only deployed to the appropriate island cluster.
Figure 23. Island Cluster Provisioning Workflow
