When a Website becomes an important business tool, companies must tackle the issues of uptime and performance. The more important a Website becomes to your operation, the less bad performance, or worse, downtime, you can afford. This explains the popularity of high-availability hosting solutions. High-availability hosting solutions provide server redundancy, both to prevent against downtime in case one server crashes and to make for faster Web page load times when all of the servers are working properly. These solutions come in a few different shapes and sizes. Some of the most popular are Round Robin DNS and Load Balancing on the Web and application server levels, and Replication, Log Shipping, and Database Clustering on the database level.
Which, if any of these, is the "right" solution for your business? That depends specifically on what you are trying to accomplish, and what's at stake.