Is your on-premise exchange availability higher than Office 365?

during my past positions and while I was supporting and maintaining infrastructures, I was always concerned about meeting the internal SLA and keeping track of the uptime and availability of the services.

Office 365 is just making our roles in the IT shop a lot easier. It is well-know that Microsoft is investing heavily in its SaaS offering, and they invest deeply in infrastructure upgrades to ensure a highly available service to Office 365 tenants.

Microsoft had released information that measure availability as the number of minutes that the Office 365 service is available in a calendar month as a percentage of the total number of minutes in that month. Microsoft called this measure of availability “the uptime number”. Within this calculation Microsoft included their business, government and education services finding the subsequent worldwide uptime number for Office 365 for following quarters:

  • Q3 – 2012: 99.98
  • Q4 – 2012: 99.97%,
  • Q1 – 2013: 99.94%
  • Q2 – 2013: 99.97%

I need to clarify that based on Microsoft documentation it is possible that individual customers may experience higher or lower uptime percentages compared to the global uptime numbers depending on location and usage patterns.

Just take a look on what ITIL Availability percentages really means for a 24/7 services.

Availability %

Downtime per year

Downtime per month*

Downtime per week


3.65 days

7.20 hours

1.68 hours


1.83 days

3.60 hours

50.4 minutes


17.52 hours /

1051.2 minutes

86.23 minutes

20.16 minutes


(“three nines”)

8.76 hours /

525.6 minutes

43.2 minutes

10.1 minutes


4.38 hours /

262.8 minutes

21.56 minutes

5.04 minutes


(“four nines”)

52.6 minutes

4.32 minutes

1.01 minutes


(“five nines”)

5.26 minutes

25.9 seconds

6.05 seconds


(“six nines”)

31.5 seconds

2.59 seconds

0.605 seconds

99.99999% (“seven nines”)

3.15 seconds

0.259 seconds

0.0605 seconds

After seeing this data, let’s think for a minute which processes do we have in place to guarantee the SLAs of our service delivery and answer the question, is your on-premise exchange availability higher than Office 365?

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