Step 11: Design Fault Tolerance
Published: November 12, 2007 | Updated: February 25, 2008
In step 5, information was collected on the → requirements for all the workloads that IT will support in the virtual infrastructure. In this step, this information is used to design the fault tolerance solutions for server virtualization host hardware. Task 1: Apply Load BalancingFor each application identified in step 5 that required network load balancing, determine how many additional VM instances of the application are needed, and then map them onto physical host systems in the same way as for the original VMs in step 9. Ideally, load balanced VMs should be distributed across multiple hosts to protect against the failure of a single host taking down all instances of the load-balanced application. Each load-balanced VM adds at least one more VM and often several to the list of VMs that need to be placed in the infrastructure. Task 2: Plan for Host ClusteringIn step 9, all the applications were mapped onto physical host servers. Count the number of physical servers that have applications requiring an MSCS cluster or host cluster as defined in step 5. This number represents the number of active cluster nodes required. Then, build an MSCS cluster plan that supports this defined number of active nodes. Each MSCS fail over cluster will require at least one additional physical host server to act as the passive node in the cluster. Validating with the BusinessAs in preceding steps related to fault tolerance, it is important to validate decisions based on input from the business. Questions should include:
Decision SummaryHost clustering can provide a simple method of ensuring that many types of VMs remain available even after the failure of a host system. The costs of implementing host clustering, however, can be significant because of hardware and storage requirements. Additionally, unused capacity on standby nodes and servers lowers overall hardware resource use. Additional Reading
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