Databases Reference
In-Depth Information
Protection from the complete failure of your primary Oracle data center site can pose
significant challenges. Your organization must carefully evaluate the risks to its primary
site. These risks include physical and environmental problems as well as hardware risks.
For example, is the data center in an area prone to floods, tornadoes, or earthquakes?
Are power failures a frequent occurrence?
Protection from primary site failure involves monitoring of and redundancy controls
for the following:
• Data center power supply
• Data center climate control facilities
• Database server redundancy
• Database redundancy
• Data redundancy
The first two items on the list are aimed at preventing the failure of the data center. Data
server redundancy provides protection from node failure within a data center but not
from complete data center loss. Should the data center fail completely, the last two items
—database redundancy and data redundancy—enable disaster recovery. In reality, this
requires data center redundancy if the goal is to run at previous production levels of
performance after the disaster.
Oracle Data Guard and Site Failures
Data Guard is an Oracle-recommended MAA solution that is used to recover databases
from site and storage failures as well as data corruption. It is included with the Enterprise
Edition of Oracle and supports database configurations for physical standby (an MAA
best practice), snapshot standby for testing, and logical standby to reduce planned
downtime. Applying redo to up to 30 physical standby Oracle databases is possible from
the primary Oracle database cascading via a remote location onto the standbys. As of
Oracle Database 12
c
, Data Guard can also be used for disaster recovery of multitenant
container databases (CDBs).
The concept of a physical standby database is simple—keep a copy of the database files
at a second location, ship the redo logs to the second site, and apply them to the copy
of the Oracle database. This process can keep the standby database “a few steps” behind
the primary database when deployed asynchronously. If the primary site fails, a standby
database is opened and becomes the production database. The potential data loss is
limited to the transactions in any redo logs that have not been shipped to the standby
site.
Figure 11-4
illustrates a standby Oracle Database.
