Total availability
Availability against the service target is a measure the business already understands.
What the published 2016 guidance says
Availability against the service target is a measure the business already understands. For each IT service, the construct divides total availability by the maximum availability, excluding the agreed downtime windows, and compares the result with the service target. Evidence is the end-to-end availability monitoring for each service. It is collected monthly. IT operations owns it, IT quality collects, and the technology lead is the client. The report shows two lines per service: the actual availability in the sampled period and the target.
What it means in practice
Availability against the service target is a measure the business already understands. Exclude the agreed downtime windows, state the measurement period, and show the actual and the target as two lines. A service with no target cannot be measured meaningfully.
Status of this record. For B.25, this page states the published 2016 guidance, not the DIS text. The DIS is at stage 40.60 and is not public. Check the published edition before you rely on the row.
What good looks like
Keep the service availability data and the agreed downtime windows. Calculate availability against the target per service. Report both lines. Review the target when the service changes.
Evidence an assessor asks for
- AvailabilityService catalogue with availability targets and agreed downtime windows
- Business continuityEnd-to-end monitoring results per service and month
The question an assessor will ask
An assessor will ask for service catalogue with availability targets and agreed downtime windows. The test for B.25 is whether that record can be produced for a live sample, not whether the guidance is described in a procedure.
Common gaps
- Component uptime reported as service availability
- Planned downtime counted as outage, or unplanned outage hidden in a window
Before the next review
Before the next review, test this against one live record: component uptime reported as service availability.
What to check when the revision publishes
When DIS 27004 is published, compare the B.25 Total availability record with this page. Ask whether the information need, the formula, the target, the frequency or the owner changes. Update the measure register and the kit, not the requirement, because the clause 9.1 duty stays as it is.