RADIUS

Planning to Fail

Having multiple servers ready to take over in case of failure is one of the most effective ways of combating downtime. Unfortunately, having multiple servers increases the total cost of ownership of the entire implementation, and many times management may want to increase availability but at the same time spend as little money as possible. However, budgeting for high availability systems is much like budgeting for any type of insurance, whether business or personal—you pay money up front for the time you will need it, but when you need it, you need it badly.

A fellow author and systems designer/administrator once told of the concept of building for failure. I find that a healthy attitude to take. Companies often build technology infrastructures involving systems critical to their day-to-day operation and then later discover the need for fault tolerance and uptime increase. Renovating an existing implementation to conform to strict availability standards is extremely expensive. However, up-front planning reduces much of this cost, and allows you to take high availability to a level that otherwise may have been cost prohibitive.

There are a few different levels, or “temperatures,” of high availability (HA), ranging from inexpensive and least timely to most expensive and instantaneously available. It’s easiest to delineate these temperatures into three groups, but that distinction made here should not be treated as a statement that other combinations of HA systems ...