What does high availability mean? In the context of what we're trying to build, it means we want our database to start and remain online for as long as possible. A critical component of this is the hardware that hosts the database itself. No matter how perfect a machine and its parts may be, the failure, of or unexpected behavior from, any element can result in an outage.

So how do we avoid these unwanted outages? We expect them. We must start by assuming hardware can and will fail, and at the worst possible moment. If we start with that in mind, it becomes much easier to make decisions regarding the composition of each server we are building.

Make no mistake! Much of this planning will rely on worksheets, caveats, and compromise. Some of our choices will have several expensive options, and we will have to weigh the benefits offered against our total cost...