This first post has to deal with what initially brought me to ITIL a couple of years ago: Availability.You have defined your Vital Business Functions, your Availability plan has been finalized, your SLAs are signed: now is showtime for some maths!
Let's start easy with the basics:
- AST = Agreed Service Time
- DT = Downtime
- TAM = Total Available Minutes for all services delivered
- TNI = Total Number of Incidents
- TNIIC = Total Number of Incidents Impacting Customers
- TUM = Total Unavailable Minutes for all services delivered
availability = (AST - DT) / AST * 100
resilience = 1 - (TNIIC / TNI)
reliability = 1 - (TUM / TAM)
Other metrics to track:
- how much unplanned costs you spent of maintaining needed availability?
- how much of your SW/HW infrastructure is supported by external vendors?
- how vulnerable are you you to security threats?
(from Incident Management:)
- what is your average response time on a customer impacting incident?
- what is your average resolution on a customer impacting incident?
Note that a lot of metrics are not related to systems uptime but to services uptime, which measurement is a challenge by itself!
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