Availability Management

Objectives:
• To predict, plan for and manage the availability of services by ensuring that:
o All services are underpinned by sufficient, reliable and properly
maintained CIs
o Where CIs are not supported internally there are appropriate contractual
agreements with third party suppliers
o Changes are proposed to prevent future loss of service availability
• Only then can IT organizations be certain of delivering the levels of availability
agreed with customers in SLAs.

Aspects of Availability:
• Reliability
• Maintainability: Maintenance you do yourself, as a company
• Resilience: Redundancy
• Serviceability: Maintenance done by someone else

Availability Information is stored in an Availability Database (ADB). This information is
used to create the Availability Plan. SLAs provide an input to this process.
Unavailability Lifecycle

MTTR: Mean Time to Repair (Downtime) – Time period that elapses between the
detection of an Incident and it’s Restoration. Includes: Incident, Detection, Diagnosis,
Repair, Recovery, Restoration.

MTBF: Mean Time Between Failures (Uptime) – Time period that elapses between
Restoration and a new Incident.

MTBSI: Mean Time Between System Incidents – Time period that elapses between two
incidents. MTTR + MTBF.

“An IT service is not available to a customer if the functions that customer requires at
that particular location cannot be used although the agreed conditions under which the IT
service is supplied are being met”

Simplistic Availability Calculation:

Agreed Service Hours –Downtime 100
------------------------------------------ X ----
Agreed Service Hours 1