Ensuring database availability is a critical skill you need even if your Oracle Database XE instance is used by a small group of developers in your department. Many types of database failures are beyond your control as a DBA, such as disk failures, network failures, and user errors. This emphasizes the need to prepare in advance for all of these potential failures after assessing the cost of database down-time versus the effort required to harden your database against failure. Many of these failures, as you might expect, require you to work closely with the server system administrators and network administrators to minimize the impact. You need to promptly receive notification when failures occur, or a warning when they are about to occur.