High Availability
Planned and Unplanned Outages
Any database may become unavailable due to a variety of planned and unplanned outages. It is prudent to pursue a high availability strategy.
Planned outages include system and software upgrades, which, as they are planned, should have little or no impact on the users.
This chapter discusses strategies to minimize downtime due to unplanned outages. Examples of unplanned outages include:
• Hardware problems including server or storage failures
• Data corruption issues due to hardware or software problems
• System outages due to power or network failures
• Data issues due to data or operational errors
The primary goal of high availability is to prevent outages. The second goal is to ensure you can recover your system after an outage. The third and for this purpose final goal is to minimize the time of any outages. The strategies discussed below attempt to minimize, if not prevent, the impact of planned and unplanned outages.
Make sure to test your prevention and recovery plans so that you know that they will work and that you are ready, when an actual (unplanned) outage occurs.