Gaining attention
Why is high availability getting so much attention?
The arrival of e-business has brought a 24 x 7 x 365 mentality to many organisations, which were previously used to eight-hour working days that left 16 hours for backup, overnight processing, and system maintenance.
Lengthened business days, the growth of B2B and B2C online transactions, and general business process reengineering have led to a general expectation that IT systems should be as reliable as the electricity supply and the phone service.
Costs vs benefits
Expenditure on high-availability systems can be seen in a similar light to insurance: you wouldn't pay AU$5000 to insure a AU$5000 car against loss or damage, so why pay an extra AU$2 million to protect against an outage that would only cost you AU$500,000?
The cost of an outage is something that must be estimated from a business perspective. In addition to any immediate cost due to transactions that cannot be performed, issues such as loss of reputation, and permanently lost customers must also be considered.
In the context of a systems outage affecting air traffic control in the UK, says John Holden, research analyst at Butler Group. "Bad news has always sold newspapers, and it will continue to do so. The fact that 100 percent of flights left on time on a particular day is not news. Similarly, the fact that a major organisation's Web site provided its customers with an uninterrupted 24 x 7 service for 99 days out of 100 is not news, but if it is out of action on the hundredth day, this will probably be news and will cause the organisation to lose current and future business."
Realistically, you're not going to get 100 percent uptime. Outages are going to occur. In assessing costs and benefits, you need to consider how often the system will fail and how long it will take to restore normal operation. It could be that a one-minute failure that occurs about once a week is acceptable, but a 45-minute outage once a year will not be tolerated. That's one reason why expressing availability as a percentage can be misleading--in this case, 99.990 percent uptime is better than 99.991 percent.
David Solsky, enterprise storage director at SecureData talks about the investment/availability curve. Each step provides increasing availability and each builds on the previous steps, but each step increases the costs.
Eric Keser, principal of Ernst & Young's technology and security risk services, points out that a business's original estimate of the longest acceptable outage should not be considered set in stone. High-availability expenditure shows diminishing returns--each marginal improvement costs more than the last. By combining the technology cost of providing particular recovery times with the business costs of suffering an outage of that duration, you may find that the lowest total cost is achieved by extending the maximum acceptable outage.
