It's that sinking feeling you get when your cell phone or pager goes off at 3:00 in the morning. No one ever calls to tell you that things are running smoothly (and if they did, they'd probably wait until a more appropriate time). No, the server has gone down ... the database server ... your server.
The problem could be any number of things. A failed disk, network problems, or power outages are among the many things that can plague you as a database administrator. However, with the right combination of hardware and software, many of these outages can be avoided.
This chapter should provide you with a basic understanding of the topic of high availability and the tools provided to help improve the availability of your databases. This chapter covers the following topics:
The definition of high availability is subjective. This is because you may have some applications that need to be available 24 hours a day, seven days a week; and you may have other database applications that only need to be available during business hours. High availability isn't always about full-time operations, but, rather, about services being accessible to your users when they need them.
High availability is also about being able to meet Service Level Agreements (SLAs) or Operating Level Agreements (OLAs), which define your requirements for maintaining application and service availability ...