SLA’s, or Service Level Agreements, establish provider commitments for service performance, availability, and reliability. When considering online services, understanding the SLA can make a world of difference.
For Google Apps Premier and Education Editions, Google offers a 99.9% availability SLA for the core services. This is based on an expectation of no downtime at all, not even for scheduled maintenance.
For Microsoft’s Exchange Online service, the 99.9% availability SLA seems comparable, but it only covers downtime outside of scheduled maintenance windows.
The difference is important since scheduled maintenance can still impact your business.
So far in August 2010, there have been two (2) scheduled maintenance windows on Saturdays, running from 12:00 PM to 3:00 PM EDT. These maintenance windows easily impact businesses that operate on Saturday, as the windows extend through the morning until mid-afternoon. And yet, they do not count against the SLAs as they were “scheduled”.
A quick check of Microsoft’s Online Service Notification feed indicates at least six (6) unscheduled outages Exchange Online over the first 23 days in August. While outages do count towards the SLAs and may result in credits, having a more reliable service is preferred.