Microsoft assembled some numbers to show that Office 365 has had almost no downtime for the last year. For four quarters in a row, the Office 365 services (hosted Exchange email, Sharepoint, Lync, and Office Web Apps) were up and running more than 99.9% of the time – between 99.94% and 99.98%, to be exact.
The uptime numbers measure all customers – business, government, and educational institutions – and cover services worldwide, with no breakdown by country or region. There may be specific individuals or businesses that fell below those marks.
It’s pretty impressive. It’s hard to keep perspective when you experience a frustrating Outlook disconnect, but on the whole Office 365 has been rock solid for the last year or more.
The blog post about the high availability talks reassuringly about the redundancy in the services:
“We build physical redundancy at the disk/card level within servers, the server level within a datacenter and the service level across geographically separate data centers to protect against failures. Each data center has facilities and power redundancy. We have multiple datacenters serving every region.
“To build redundancy at the data level, we constantly replicate data across geographically separate datacenters. Our design goal is to maintain multiple copies of data whether in transit or at rest and failover capabilities to enable rapid recovery.”
One interesting way to think about the high availability: if you’re a small business with an onsite mail server, the chances are that its availability has been less than 99.9% because of the time spent installing patches and restarting.
In 2013 Microsoft has been upgrading the Office 365 servers to new versions of Exchange, Sharepoint, etc., that are better designed for cloud access and high availability. I’d expect the uptime numbers to improve as the service continues to mature.