Office 365 availability: A moveable feast

Danny Bradbury

How much can you trust Office 365 to preserve your email access? The answer is, not as much as you might think. Just using Office 365 alone for your email could leave you scurrying for access in the event of an outage.The company has been transparent about its uptime figures since 2013, when it released top line reports for the service dating from the second half of 2012. Here they are:

But how relevant are those figures to customers, really? It all depends what you’re measuring, and how. Office 365 outages happen frequently – and when they do, they can take down email access for long periods of time. Take the Exchange Online outage in June 2014, for example, which saw the service go down for nine consecutive hours, with patchy communication from Microsoft leaving customers confused and frustrated.

Q3 2012 Q4 2012 Q1 2013 Q2 2013 Q3 2013 Q4 2013 Q1 2014 Q2 2014 Q3 2014 Q4 2014 Q1 2015
99.98% 99.97% 99.94% 99.97% 99.96% 99.98% 99.99% 99.95% 99.98% 99.99% 99.99%


Based on that outage, eagle-eyed readers will spot an immediate problem with the 99.95% availability figure for the service in Q2 2014.

In our post on business continuity, we outlined what availability figures really mean in hours, minutes and seconds. On a quarterly basis, 99.95% uptime equates to one hour, five and a half minutes. So where did almost eight other hours of downtime go that quarter?It’s difficult to say, because while Microsoft has made a great show of releasing regular, public top line data about service availability, it doesn’t release the details. That makes it difficult to get data about how many customers were affected, and when, during that incident, or others.

Microsoft’s definition of service levels also give it the opportunity to classify outages under different terms. For example, the company uses “service interruption/outage” to describe a service that is “slow, sluggish, or occasionally unresponsive for brief periods”. Other terms include “extended recovery”, which can lead to poor performance in services that are technically still ‘up’.

On paper, then, Microsoft’s uptime figures for its Office 365 service may seem acceptable. But the concept of uptime doesn’t necessarily mean what some customers may assume it means. And in any case, that SLA is only financially backed at 99.9%, meaning that the company doesn’t technically speaking have to pay out if it meets a target which may already be misinterpreted by customers.

This isn’t the first time that the company has reported outages with its service. For example, in February 2013, Office 365 went down over a period of hours, leading it to drop its uptime figure to 99.94% in Q1 that year. This followed an outage with its online Outlook service in January. In 2012, it saw outages on November 8 and 13th, sending customers a formal letter of apology in response, crediting customers with 25% of the monthly invoice automatically to placate them.

What this means for customers is clear. Relying purely on Office 365 could render them vulnerable to disruptions in their IT service. Email is the lifeblood of any company, and could be considered a mission-critical application by many. Any other critical IT service would be protected by some kind of contingency. When your email is in the hands of a service provider with a somewhat opaque approach to outages, it makes sense to use an alternative for business continuity purposes.

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