VCAP-DCD |Objective 2.3 | Build availability requirements into the logical design

Understand what logical availability services are provided by VMware solutions.

The two primary availability services in vSphere are High Availability (HA) and Fault Tolerance (FT). Studying for this exam, you should be understand the differences in these features, however at a very high level: HA – Can minimise downtime by restarting VMs in case of a hardware failure FT – Provides continues availability for a VM by making a secondary copy of the VM on another physical host. To gain a better understanding of VMware’s HA, (as well as DRS, Storage DRS and Stretched Clusters) the VMware vSphere 5.1 Clustering Deep Dive by Frank Denneman and Duncan Epping is a MUST! The VMware vSphere Availability Guide is also a MUST read. Fault Tolerance, whist no doubt is a great technology, it does have limitations, which are discussed in the Availability Guide. I rarely see a business case for FT, in most cases HA is good enough.

Identify and differentiate infrastructure qualities (Availability, Manageability, Performance, Recoverability, Security)

Availability – The ability of a system or service to perform it’s required function when required. It is usually calculated as a percentage.

Manageability – The expense of running a system. If in a large enterprise the system is managed by a small team, the operation cost can therefore be low.

Performance – The measure of what is delivered by the system. This is usually measured against known standards. Recoverability – The ability to return a system to a working state after a failure or repair.

Security – The process of ensuring the service is used in the appropriate manner.

Describe the concept of redundancy and the risks associated with single points of failure.

A single point of failure is a system component, that if it fails, will then cause the entire system to fail because of it. For example, in a vSphere world, if we have a virtual switch with a single physical NIC uplink and this uplink fails, the virtual switch will fail as a result. These components can be bolstered by adding redundancy, in the above example we could add redundancy to the virtual switch by adding a second physical uplink, therefore if one uplink fails traffic could continue to pass on the second uplink. This spreads out to multiple areas of a vSphere design, hosts in clusters, components in hosts and stretching out to the wider infrastructure, with multiple physical switches, load balancers etc etc.

Differentiate Business Continuity and Disaster Recovery concepts.

Business Continuity is focussing on avoiding or mitigating the impact of risk, therefore is a proactive approach.

Disaster Recovery is focussing on the recovery of a system/service after an outage, therefore is a reactive approach.

VMware offer a free DR/BC Fundamentals training course through MyLearn. Click the following link to register

DR/BC Fundamentals



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