Paul DeGroot, consultant at Pica Communications
Contracts can be confusing though. DeGroot says sometimes relevant information is in a supporting document. SLA parameters can be outlined in one section of a document but the contract can be subject to terms that are defined in other literature. Make sure to read the entire contract, including any supporting documents.
Some providers will automatically credit customers when there is an outage, others will not. It is imperative that customers report any outages they believe breach the SLA. DeGroot has run into instances where customers experienced a multi-day outage and were sure their bill would simply reflect the event with a credit. But if you don't document and report it, you don't have any way to prove you experienced downtime. If you have a problem, record it, inform your provider immediately and file a claim for the breach of an SLA.
Microsoft requires that customers submit an SLA breach claim to customer support by the end of the calendar month after the event has happened. (So for example if an incident happens in mid February, the customer has until the end of March to report it.) The claim must include: a detailed description of the incident; duration of incident; number of users or sites impacted; description of your attempts to remedy the situation.
Many of Microsoft's services come with a 99.9% uptime guarantee (three-nines). That sounds good. But being up for 99.9% of the year still allows for 8 hours and 45 minutes of downtime each year with no breach of the SLA. How would you feel if your workload is unavailable for 8 hours one day? This uptime calculator can help users predict how much downtime they should expect from their provider based on their SLA uptime guarantee.
Each individual service can have its own SLA uptime guarantee. For example, Microsoft Azure VMs have a 99.95% uptime guarantee (if deployed across two Availability Sets; more on that later) and the SQL database has a 99.9% uptime guarantee. Most Microsoft Online SaaS products come with a 99.9% uptime guarantee too. But 99.9% uptime allows for up to 43 minutes of downtime to occur in a month without breaching the SLA.
As Troy Hunt, a Microsoft expert blogger points out in this piece, those downtime events do not have to occur at the same time for the provider's SLA to be intact. So, for example, if you have a system that relies on Azure VMs, a SQL database and Azure storage, then on the first day of a month an Azure VM could go down for 21 minutes and bring your workload down. The next day Azure SQL could go down for another 42 minutes and bring the application down. Both of those would still be within the terms of the SLA. For more on this, blogger Brent Stineman explores how to calculate aggregate SLAs across multiple services here.
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