Microsoft will notify customers of what it calls "disruptive changes" to its core products, notes Donald Retallack, a research vice president at Directions on Microsoft, a consultancy. Microsoft defines "disruptive changes" as: "change(s) where a customer or administrator is required to take action in order to avoid significant degradation to the normal operation of the online service." Microsoft promises to inform customers six months in advance of a disruptive change to its Dynamics CRM platform, for example. But other non-disruptive changes can occur without Microsoft notifying customers.
It is one thing for a service to go down for an unexpected reason, but sometimes the cloud can go down because the service providers take it down. Verizon, for example, had an almost 48-hour planned outage earlier this year. Outages like that can mean the service is down, but it doesn't count against the SLA. Customers can ask their provider to ensure they will be informed of any planned downtime.
Many providers offer free-tiers of service or other products that are in preview. Typically, those free and preview services are not covered by SLAs. So, feel free to use them but make sure you understand the terms and the risks of using them before relying on them for critical functions.
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