One of the great benefits for us in IT is that as hardware and storage prices have come down, and performance has increased, we are more able to offer services that in the past was prohibitively expensive to deliver. Rapid deployment and expansion of service, redundancy, and very high availability are all possible now for a fraction of the cost of a few years ago. Granted, it still costs more to provide such high quality service. Let’s take a look at how virtualization, replication and high availability, impact storage requirements and costs.

Virtualization allows us to deploy servers without tying resources to a single specific hardware system. The images can be moved from one system to another, cloned, made redundant and thereby easily allow expansion of particular applications and services. Virtual servers are a foundation for simple, rapid, consistent scalability. Having several or many identical instances allows us to deliver high availability far more easily. Virtual images do take space, and must run on a base platform, so clearly a single VM takes more space and resources that the same service running on dedicated hardware.

High Availability (HA) is the IT goal of having continuously available service for a particular application, connection or resource. Sometimes this is done via fail-over from a primary to a secondary connection or resource. It is also possible via load balancing. The load balancing can be accomplished at the application layer, at a gateway layer, or via an appliance. Load balancing is also possible at the name lookup level. For the purposes of this discussion we are considering application, gateway, and appliance types of load balancing and fail-over. Application layer mail gateway routing is often built-in to the system, whereby the gateway has alternate choices to try if its primary gateway is unavailable. This may be implemented in different ways depending on the vendor and the service. For SMTP there are underlying standards and requirements for gateway and routing behavior.

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