Microsoft® SQL Server 2012 Unleashed

What Is High Availability?

The availability continuum depicted in Figure 39.1 shows a general classification of availability based on the amount of downtime an application can tolerate without impacting the business. You would write your service-level agreements (SLAs) to support and try to achieve one of these continuum categories.

FIGURE 39.1 Availability continuum.

Topping the chart is the extreme availability category, so named to indicate that this is the least tolerant category and is essentially a zero (or near zero) downtime requirement (that is, sustained 99.5% to 100% availability). The mythical five-nines falls at the high end of ...