As a database administrator, your primary job is to keep the database up and running
during specific time periods, which are usually outlined in a service level agreement.
This service level agreement probably specifies the amount of uptime your system must provide,
as well as performance rates and recovery time in the event of a failure.
In fact, a variety of types of failures can occur in a complex computer system, including the following:
* Disk drive failure
Disk drive technology has improved,
but a disk drive is still a mechanical device and, as such, is subject to wear.
The disk drive is one of the most common areas of failure.
* Hardware component failure
Hardware failures can occur because of wear and tear on the components, primarily from heat.
Even the best-made computer equipment can fail over time.
* Software component failure
Some software flaws are discovered only under rare conditions.
Your system might run for months or years until a specific set of conditions uncovers a problem.
In addition, adding applications to a stable environment
might modify a critical library or file and cause problems.
* External failure
A system can fail because of external causes, such as power outages.
Whether your system can survive such a failure depends on
whether you are using an uninterruptible power supply (UPS) and redundant power sources.
* Human error
Clustering does not usually protect a system against failures caused by human error
(such as accidentally deleting a table or a Windows NT file system partition).
Source:
Microsoft SQL Server 2000 Administrator's Companion eBook