Sunday, May 16, 2010

What is Service Availabiltiy?

The following is an excerpt from a comment posted on a TechRepublic forum in 2008. The topic, however, remains relevant:

By now, we should all be aware that Availabiity should be measured by Service. This means that if there are several systems necessary to deliver a service (email, internet access), we should measure the average uptime of all system components required to deliver that service. In doing so, we can arrive at a predictable level of uptime.

This is the baseline used to determine the improvements necessary to meet customers requirements and expectations regarding availability. If a higher level of availability is required, then additional components (bandwidth, storage, memory) can be added to reach the desired level of availability.

Additionally, availability is always relative to the timeframe in which it is measured. This means that a service that requires 99.999% availability between the hours of 9-5 (M-F) may be much different (in terms of architecture & resource requirements) than a service that requires the same level of availabilty 24/7. Thus, not every service requires the same level of availability.

This concept of relative availability is one that is always missing from the discussions of uptime.

What is also missing from these discussions is a definition of "uptime" and the impact of performance on that definition.

If a service is available but very slow, is it still considered "up?"

Here is where the specifics in a Service Level Agreements become very important.

The ITIL library provides guidance on these and other IT Service Management process disciplines.

ITIL & IT Service Management

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