Comparing the severity of IT service outages: Uptime Institute's Outage Severity Rating

Overview

Published by A. Lawrence in the Uptime Institute Journal in 2019, this article introduces Uptime's five-category Outage Severity Rating. The scale aims to make the business impact of an IT service interruption comparable whatever its technical cause. The author likens the approach to the Beaufort scale: rather than a measured quantity, it is a qualitative rating that classifies the impact actually experienced.

The scale has five steps running from negligible to severe (Category 5). Each category describes business impact without regard to cause, so a power failure and a software fault can be compared within the same frame. This tries to get past the limits of reducing outages to a single yardstick such as duration or the number of affected users. The article applies the scale to public outages between 2016 and 2018. In that period, 11 outages were tracked as Severe (Category 5) and 46 as Serious (Category 4). Five of the 11 severe outages occurred at airlines. When Categories 4 and 5 are combined, banking and financial services is the most over-weighted sector relative to its share.

The scale's limit is its qualitative nature: the categories are a judgement-based classification rather than a precise calculation, and the analysis covers only outages that became public. Even so, the scale gives managers and engineers a shared vocabulary for discussing outage risk. In data centre design, that vocabulary can express incident severity consistently in risk registers and outage-cost estimates.

Key points

1. The scale defines business impact in five categories, from negligible to severe (Category 5), regardless of cause.
2. The rating is qualitative and is compared to the Beaufort scale.
3. In 2016-2018, 11 Severe (Category 5) and 46 Serious (Category 4) public outages were tracked.
4. Five of the 11 severe outages occurred at airlines.
5. Banking and financial services is the most over-weighted sector when Categories 4 and 5 are combined.
6. The article appeared in the Uptime Institute Journal in 2019 and is freely readable.
7. The analysis covers only publicly reported outages.

Using it in design

• Express incident severity in the risk register on a 1-5 scale.
• In the outage-cost estimator interface, map the user's scenario to one of the five severity categories.
• Compare outages with different causes (power, cooling, software) on a common impact scale.
• For high-impact sectors such as finance and aviation, define the target severity category as a design requirement.

Who should read it

Data centre engineers and risk managers who prepare risk registers and outage-impact assessments.

Publication details

Authors

A. Lawrence

Publisher

Uptime Institute Journal (Uptime Institute)

Year

2019

Document language

English

Source type

Industry body

Access

Free to read

Licence

Copyright retained; citation only — the publisher’s terms apply to the original document

Citation