- The Service Level Agreement
- Helping Users Identify Their Availability Requirements
- Availability Levels and Measurements
- Quantifying Availability Targets
- Availability: A User Metric
- Measuring End-to-End Availability
- Summary
- Harris Kern's Enterprise Computing Institute
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Helping Users Identify Their Availability Requirements
Ask users the following questions to help identify their availability requirements:
What are your scheduled operations? What times of the day and days of the week do you expect to be using the system or application?
The answers to these questions help you identify times when your system or application must be available. Normally, the responses coincide with users' regular working hours. For example, users may primarily work with an application from 8:00 a.m. to 5:00 p.m., Monday through Friday. However, some users want to be able to access the system for overtime work. Depending on the number of users who access the system during off hours, you can choose to include those times in your normal operating hours. Alternatively, you can set up a procedure for users to request off-hours system availability at least three days in advance.
When external users or customers access a system, its operating hours are often extended well beyond the normal business hours. This is especially true with online banking, Internet services, e-commerce systems, and other essential utilities such as electricity, water, and communications. Users of these systems usually demand availability 24 hours a day, 7 days a week, or as close as possible.
How often can you tolerate system outages during the times that you're using the system or application? How often can you tolerate scheduled outages?
Your goal is to understand the impact on users if the system becomes unavailable when it's scheduled to be available. For example, a user may say that he can only afford two outages a month. This answer also tells you whether you can ever schedule an outage during times when the system is committed to be available. You may want to do so for maintenance, upgrades, or other housekeeping purposes. For instance, a system that should be online 24 hours a day, 7 days a week may still require a scheduled downtime at midnight to perform full backups.
How long can an outage last if one does occur?
This question helps identify how long the user is willing to wait for the restoration of the system during an outage, or to what extent outages can be tolerated without severely impacting the business. For example, a user may say that any outage can only last for up to a maximum of three hours. Often, a user can tolerate longer outages if they're scheduled.